T8700 as you have already been advised is better than T6500 in terms of frequency and power consumption and I see that you are opting for it already which is good to know however I'd just like to make a couple of corrections here.
First of all, the CPU model is T8500, I saw your post and the reply stated P8700.
Secondly, when you said "i want to know whether p8700 core 2 duo mobile processor is powerful thean t6500 or is it really less powerful because of the lower watttage", please remember that lower wattage means better consumption of power saving electricity and cutting down your electricity bills supporting a greener environment that we talk so much of now. Lower wattage is always good and lower watts does not mean that it is going to lessen the frequency of a CPU.
Hope this helps, best of luck and thank you for choosing Intel!
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