Upgrade from Q6600 to i5-3470

The CPU will not fit that motherboard, which is designed for earlier sandy bridge models. Get the cheapest H77 board you can find froma good brand ( Asus, ASRock, Gigabyte, MSI) and upgrade your PSU, that one looks EXTREMELY sketchy and 400W is pushing the limits.

The CPU is on the supported CPU list, starting with BIOS version F7.
That BIOS is available for download, the very first one released.
What you you recommend from the other motherboards ?
Gigabyte H77-DS3H
Gigabyte Z77-DS3H
Gigabyte Z77M-D3H
Asrock Z77 PRO3

The H77-DS3H. Try the Antec Earthwatts Green 500W PSU, it's around $50

Sorry, Antec is out of my price range : $71 - $136
I can only buy from one specific website, I have a large discount code.

Lots of other users, on another forum, recommended Sirtec PSUs.

Other options are:
Thermaltake Litepower 400W / 450 W
Rasurbo 400 / 450 / 550 / 650 (not very recommended on other forum)
Delux and Floston - they look like cheap ones, despite the same price range

There's no reason to get such a PSU as that unless OP wants to upgrade to a high end graphics card such as a Radeon 7870. Sirtec makes a lot of great power supplies (many Corsair/Antec models are made by them), but I think that I'd recommend something like a good Seasonic or Antec 350-360W model for OP, assuming that OP doesn't want to upgrade the graphics to a good gaming card or do some other high power consumption upgrade.

H77 is not inherently better than B75 in most ways, but it has a few advantages such has better IGP support and one more native third generation SATA port. Z77 is just H77 with additional overclocking features and SSD caching features. There aren't any performance differences other than feature differences AFAIK.

Motherboards generally don't impact how fast a system is except through better overclocking headroom, but some can have some faults that make systems less responsive. However, it's difficult to predict what boards have such faults without testing them and most boards aren't tested for such issues.

For example, some Gigabyte boards have been known to have issues, yet other Gigabyte boards have been among the best about this. They do tend to have the worst chances for it among the more popular motherboard companies, but that doesn't stop the chances from being quite small. Asus has been known to be a little more finicky about memory than most other companies, but again, that's usually not an issue either. All of the companies have had their quirks in the past AFAIK.

Seasonic is also out of my price range: $86 - $204.
No, no upgrade for video card any time soon.

I do not need IGP.
Maybe I will upgrade the 2 x 250 Gb HDD to one 1 Tb driver in the next 6 - 12 months, so better SATA port may be useful.

Seasonic can be as cheap as the other companies if you know what to look for. Also, notice how I suggested Antec as well, not just Seasonic, and you can find Antec in the $30-50 range pretty much anywhere. Still, OP, your current choice shouldn't cause any issues. Sirtec is a good PSU manufacturer (unlike most PSU companies, Sirtec actually makes their own PSUs themselves and they generally do a good job of it) and their work is usually top-notch or near top-notch.

The i5-3470 has an IGP. It's not as powerful as the GT 440, but it is there and B75 and H77 boards all support it. Unless you use the GT 440 for anything that the IGP can't handle (going by what you've said so far, that seems unlikely), you might want to actually forgo it and use the IGP instead to save power.

It might be useful to have a second SATA 6Gb/s port if you get a SATA 6Gb/s hard drive, but just be aware of the fact that even SATA 1.5Gb/s is generally not a bottle-neck for even today's hard drives and SATA 3Gb/s is almost never a bottle-neck at all for today's hard drives. I'm not saying that there's anything wrong with upgrading the storage, but I am saying that you shouldn't expect a noticeable difference between using a hard drive on a SATA 3Gb/s port and on a 6Gb/s port even if its a SATA 6Gb/s hard drive. Well, maybe future hard drives will change this, but not today's models.

As I said before: I can only buy from one specific website, I have a large discount code.
They only have 4 models of Antec and Seasonic, in those price ranges.

So, in the end, Sirtec is OK and 400W is enough.

Is there a way to find out the factory default BIOS version or a [Gigabyte] motherboard ?
One uses above said i5-3470 is not supported [out of the box] by Gigabyte B75-D3V motherboard.
But it is, from F7 BIOS above.
And it's the exact same situation with the H77-DS3H - official site says CPU is supported from F7 BIOS and above.
F7 and F8a BIOSes are available for download.

The only way to know what BIOS version they ship with is to buy one and check. They are usually out of date, but motherboards sometimes get updated before shipping and even if they don't, who's to say how out of date they are? Even if you get one that doesn't support your i5-3470 out of the box, most stores will update it for you for free it you ask. You could check with the store that you're buying from or you could instead buy a model that is known to support the i5-3470 out of the box.

If pricing on everything other than Sirtec is that bad, then yes, stick with the Sirtec model that you picked out earlier.

All right, thanks guys for the info.

Glad to help.

Tomorrow I'll place the order.
I'll get this motherboard: Gigabyte B75-D3V
http://www.emag.ro/placa-de-baza-gigabyte-socket-1155-b...
It has EFI BIOS and Dual BIOS, PnP 1.0a, DMI 2.0, SM BIOS 2.6, ACPI 2.0a
I won't have any problems, because of EFI, to install Windows 7 x64 on my SSD using MBR, right ?!

You wouldn't have any problems with that AFAIK.

Just to throw in expected performance increases, I went from a Q6600 to an i5-2310 and every app and bench I throw at it performs almost exactly twice as fast on the new i5. 3470 is probably 10-20% faster still, so I would expect at least a 100% increase for most tasks and probably more.

Yes, that doesn't seem like an outlandish expectation for CPU performance improvement.