i have a acer aspire ax3950 with 8Gb ddr3 ram, intel core i3 550 at 3.19 GHz and a AMD redeon HD 6570 1GB, core clock at 650Mhz and memory clock 1000Mhz, on a resolution of 1024 x 768 it can run planetside 2 at around 40 fps and 17 fps in mid battle, and BeamNG drive at around 25 fps at low graphics. it has i think a 220 watt power supply, are there any GPU's out there that will run these games better where I don't need a new PSU, money or space is not an issue but I won't spend $500 on this PC when I can add $1500 to that and build a PC that will last me 5 years of running the newest games at high graphics. I will spend up to $500AU if I can find a new PSU and GPU, but I don't expect it to last me 5 years I will eventually buy a new one but should I buy it now or upgrade this and wait. It only has one slot which my GPU is sitting.
If you only want to upgrade you gpu, your biggest problem is your PSU. Apart from that, getting a new gpu is the best bet for you. Do you have space for a two slot gpu? What kind of budget do you have?
Looking at your case, i would guess that it is difficult to fit a new psu in it. You could of course update case+psu+gpu, and go for a full size gpu, but if you do not wish to upgrade the psu, I would not recommend putting a new gpu in that machine.
Ok, lets unravel this.
The card you currently have actually requires a 400W power supply. It seems aspire was saving money on giving you less, but it might not be a problem, as gpu producers usually have a bit high wattage as minimum to make sure people can use the hardware. You CPU uses a maximum 73W, so even with a card that uses the maximum 75W available on the PCIE slot should be fine.
Your card uses 50W. You can either buy a GTX750 (which uses 55W and is a bit cheaper) or the GTX750ti(which uses 60W and is 15-20% faster). There isn't really any low power alternative with gaming performance by ATI atm, so you have to go NVIDIA. The 750ti might be pushing it a bit, but your PSU should still handle it with ease (NVIDIA recommends at least 300W, but they are playing it safe there).
The only problem is that the 750ti is usually a two slot card. If you do not have two slots, and are good at diy, see this article http://www.tomshardware.com/reviews/single-slot-geforce... if you do not want to mess with things, get the 750. But be aware that the 750 is not really made for gaming, and the 1gb ram on the gpu might be a problem even at your resolutions. I think galaxy has announced a single slot 750ti, but it is not released.
Estimating the performance increase of this is difficult, but your card is MUCH slower then the 750ti. In the gpu-ranking you are 8 tiers below the 750ti and 6 tier below the 750, where one tier is ~10% http://www.tomshardware.com/reviews/gaming-graphics-car... . If you want to play now, either upgrade now or buy new now. If you can wait (although I wouldn't at 17fps mid battle ), then waiting and saving will obviously buy you a better machine when you have the money. But this is defiantly a worthwhile upgrade!
Build you a list of the things you need. Your case is small and your PSU needs upgrading for any potential GPU upgrades. That being said you still need to upgrade your CPU to prevent bottleneck. All in all you need a complete re-haul, however this list remains within your $500 limit and acquires you the best money can buy disregarding your CPU's capabilities.