Is 1 stick of xms 3000cl2 512megs

What would you use ,i have 1 stick of corsair 512megs xms3000 cl2,and a stick of kingston 512 cl2.5 .would i get better performance using just the corsair or using both for more total memory "1 gig ,my sandra score drops with both in by 100.so what i am getting at is do i go for better memory bandwith or more total ram 1 gig verses 512 thanks.....................

You'll get better performance just using the Cosair. You'll get more memory with the 2 sticks (obviously). Performance of 2 sticks will be limited by the slowest stick.

I would use both sticks if the kingston can run cas 2 also. More ram wont speed benchmarks up but it will help your multitasking greatly.