Want to upgrade my gpu..

Alright. My story is that I started playing SWTOR about a week after it came out, my old computer ran it horribly at around 15-25 fps. I got mad, bought a new computer. The bad part is that the only way i could afford that is putting it on my Dell credit card. I bought a Dell XPS.

My specs on this are:
8 GB Ram
Intel i7-2600 CPU @ 3.4GHZ
AMD Radeon HD 6670 1GB GPU
Core Clock@ 800 Mhz
Memory Clock@ 1000Mhz

My problem.. It runs the game fine and I was happy with it. Until my friend bought the exact same computer because he liked mine, but decided to get the more advanced video card. Mines the 6670, he got the 6770. My SWTOR on max settings is running about 40-60fps, while his is running at a steady 110 fps just because of that card.

My problem is, that of course, Im jealous. Should i just buy that exact card? Or is there one that will top him that i can buy for a little bit more (the 6770 is a little over $100) Id spend about $150 or so just to top him. Also I need to make sure it will fit in my XPS and be compatible. Help plz!! Im not that experienced!

What make/model is your power supply? Measure to see if you have enough room in your case for a new card, maybe a 6870 or similar

Well i should be able to fit most video cards. Not huge ones. Not sure what power supply it is. The computer is a Dell XPS 8300. 460W power supply (max). The 6670 fits fine, it might clip the ram a little bit but depth i have plenty of room.