Will GTX 560 Help my OLD Dell XPS 720?

[SdS49r]

Hi all! I've got an old Dell XPS720 and can't afford a new rig for a few years, or untill the economy gets better. Also can't change Motherboard due to the BTX form factor and proprietary power supply. Any way the Specs are as follows:

Dell XPS 720
Core 2 Extreme CPU Q6800 @ 2.93GHz
8 GB DDR2-SDRAM Ram
GeForce 8800 GTX 768 MB
750 Watt PSU
Windows 7 Pro 64-bit

COD runs but all settings are midrange. Would love to bump these up alot higher. Iv'e been looking at several cards and would like your opinions about the performance COD improvment I might see with these. Also any opinion about other video cards given my system. Here's what Ive Been looking at:

EVGA GeForce GTX 560 2048MB Superclocked
Core Clock: 850Mhz
Memory Clock: 4008MHz
Shader Clock: 1700MHz
RAM: 2-GIG
RAM Type GDDR5


EVGA GeForce GTX 560 Ti Superclocked
Core Clock: 900Mhz
Memory Clock: 4212MHz
Shader Clock: 1800MHz
RAM: 1-GIG
RAM Type GDDR5

Thanks for your comments.