£90-£100 upgrade. CPU or GPU?

[grumpycrab]

My Motherboard is an ageing ASUS P5NE-SLI and I feel like some retail therapy.
I can either add to my existing GeForce 8800 GTS 320MB to give me SLI or get a new CPU (my current E4300 is overclocked to 2.7GHz).

What should I do? Cheers.

 

[grumpycrab]

Thanks for the replies guys...Memory is OCZ 2x1GB PC2-6400 Dual Channel; game res 1280x1024. I will try and push the E4300 further. I've just reinstalled it as it was unstable 'cause I used too much thermal compound. Stupid mistake...but I have a Tuniq so will try and push the CPU to 3GHz.