P5B will work fine at stock speed inverted. But like most people who will overclock the conroe, its best to mount put a 40-60 mm sized fan blowing onto the NB if you want to use it inverted..
Most E6600 will do 3.2GHz at less than 1.4V Vcore....(Othros Stable).
I use Corsair TwinX 2048 DDR2 6400 5-5-5-12 on mine... With a E6600, its good up to 3.6GHz.
As for the Asus P5B vs the Gigabyte GA-965-DS3.. I choose the P5B becuase it leaves more clearence from the bottom of the motherboard compartment in a LL -V series case. (I suspect the gigabyte will be a very very tight fit with a 120mm (Tower 120, Ultra120) heat sink in a LL-V series case.)