Upgrade CPU or GPU?

[magicoi]

I use my PC for mainly gaming and ARMA 2 doresnt look or run nice enough for me with current specs. I've been toying with the upgrade idea for a while and prices for GPU's are very attractive now, as for CPU's....i think it would be a bottleneck but im not savvy enough to know for sure! HELP""

CPU: E4500 @ 2.91Ghz
8800GTX - stock clocks
Asus P5K Lifestyle mobo
4Gig PC8500 RAM
XP

The 4890's look good as do the 260's but i just dont know if its a wast without doing the CPU first.

Suggestions please

 

[magicoi]

currently 1440*900 but a 24" will follow shortly so i need something with some omph!

 

[magicoi]

right, the deal of the week it is then, that ought to see me through:
Asus GeForce GTX 260 TOP

Followed in due course by a new CPU and monitor!