GT630M better than the GT555M in y570?

Not really. GT 630m is a rebadge GT 540m.

The GDDR5 version definitely looks a bit faster than Lenovo GT 555m. But the DDR3 version does not look like it is.

However, the performance difference will be very small.

GT 540m 96:16:4 672 1344 1800
GT 555m (Lenovo) 96:16:4 753 1506 3138
GT 630m DDR3 96:16:4 672 1600 1800
GT 630m GDDR5 96:16:4 800 1600 3600

The GT 555M in the Lenovo Y570, while not as fast as the true versions of the GT 555M used in the previous generation Alienware M14x and the Dell XPS 17, is faster than the GT 630M (GT 540M).

However, the Y570 is not a particularly good laptop to buy in the general case, because it has a 15.6" 1366x768 display. 15.6" 1366x768 and 17.3" 1600x900 displays make things onscreen large, and tend to have very poor image quality due to low contrast. I recommend not to buy laptops that come with this type of display to those who have a budget that allows them to get a laptop that has a better display and still suits their needs, and who don't require larger text for eyesight-related reasons.

Consider this HP DV6-6C53NR. It has a 15.6" 1920x1080 matte display, and an AMD Radeon 7690M XT which is as fast as the true version of the GT 555M and is faster than the GT 555M the Y570 comes with. This laptop comes with an i5-2450M processor, and in case the laptops you were looking at have Core i7 processors, keep in mind that the processor is not something you should prioritize over the GPU and the screen unless you have a particular need for a fast processor. Game performance depends more on the GPU than it does on the CPU.

And ensure that, if you get the HP DV6, that you go into the BIOS and change the switchable graphics setting from DYNAMIC to FIXED. Some games will not properly engage the dedicated GPU under dynamic mode, such as Minecraft and a few others. FIXED gives you manual control over which GPU is enabled, and it should ask you to change enable the dedicated GPU when power is plugged in and disable the dedicated GPU when power is unplugged.

Contrast has nothing to do with screen resolution.

Contrast depends on the panel technology. The vast majority of laptops use TN panels and while they are generally stated to have a 1000:1 static contrast ratio, the true contrast is generally lower at around 700:1 or at best 800:1 based on general reviews of TN panel monitors.

Contrast is not implicit of screen resolution, but most 15.6" 1366x768 and 17.3" 1600x900 displays are low-end LCD panels that tend to have poor contrast due to being manufactured cheaply. 15.6" 1600x900, 15.6" 1920x1080, and 17.3" 1920x1080 displays tend to have much better contrast because LCD manufacturers will put more emphasis on screen quality into higher end panels. Two exceptions to this are the Samsung Series 7's 1600x900 LCD, and the AUO B156HW01 V5 FHD LCD that ASUS used in a number of their G-Series and N-Series before they started using matte screens.

Other issues common with 15.6" 1366x768 and 17.3" 1600x900 displays that are not typical of their higher DPI counterparts are graininess, slightly poorer viewing angles, and dark color gradiation due in part to the poorer viewing angles.

All of these issues are also typical of the majority of displays 14" and below, regardless of resolution, and it is difficult to find a laptop that offers a resolution higher than 1366x768 and/or better image quality in these sizes.

Laptop manufacturers do not have exclusive contracts with LCD panel producers, they generally tend to purchase LCD panels from a number of producers based on supply and demand. For example, AU Optronics' TN panels are generally high quality than Chi Mei's TN panels, but they can end up on the same laptop model. Also, quality can vary from the same manufacture based on the plant of the origination.

For example, Samsung panels manufactured in Korea seems to be of higher quality than compared to those manufactured in Mexico. Their plant in Poland seems to produce LCD panels who's quality is somewhere between from Korea and Mexico. This is based on Samsung TN panel comparisons done by someone from Hardforum.com.

But if you take a look around NotebookCheck laptop reviews of various laptops with different types of displays, then you will find that higher-than-standard resolution LCD panels in the 15.6" and 17.3" sizes tend to have appreciably higher measured contrast ratios than the standard resolution LCD panels do, mostly independent of manufacturer. There tends to be a larger difference between the image quality of a 15.6" 1366x768 display and a 15.6" 1920x1080 display from one manufacturer, than between two identical-resolution displays that come from different manufacturers.

http://www.notebookcheck.net/Review-Asus-N53SV-Notebook...
- Samsung 15.6" 1366x768
- 172:1 measured contrast

http://www.notebookcheck.net/Review-HP-Pavilion-dv6-600...
- Chi Mei 15.6" 1366x768
- 192:1 measured contrast

http://www.notebookcheck.net/Review-Asus-N53SN-X5MSN-No...
- LG 15.6" 1366x768
- 166:1 measured contrast

http://www.notebookcheck.net/Review-Dell-Latitude-E5520...
- LG 15.6" 1366x768
- 136:1 measured contrast

http://www.notebookcheck.net/Review-Dell-Latitude-E6520...
- LG 15.6" 1920x1080 (LP156WF1 XX XX)
- 669:1 measured contrast

http://www.notebookcheck.net/Review-Dell-XPS-15-Noteboo...
- AUO 15.6" 1920x1080 (B156HW01 V7)
- 646:1 measured contrast

- http://www.notebookcheck.net/Review-Lenovo-Thinkpad-T52...
- Unknown manufacturer, 15.6" 1600x900
- 670:1 measured contrast

well thanks for the update - it turns out the y570 is gone where i was going to buy it so it sort of makes the decision easier

the dv6 in the link i can get for 795 and for another 5 euro i can get an msi with a GT650M in it which i was looking at - it has a good screen too which i would get in a heartbeat. i hadn't really given much thought to the screen to be honest. was more concerned with buying a laptop with outdated gfx.

i am looking at these 2 laptops now and have to justify the spending of an extra 250 just for games performance and longevity

packard bell i5 2450 4gb 640gb gt630M (2GB model) for 550 euro or an acer equivalent for extra 20 euro

and the

msi i5 3210 4gb 500gb gt650m 800 euro

250 seems a bit steep just for the graphics card upgrade but ill have a think about it.