yes, the new prime95 (v25.6 i believe) will automatically find all your cores.
depending on what you want to test there are 4 types: Blend, small FFT's, Large FFT's, Custom
blend: everything tested, a lot of RAM used
small: mostly processor, not a lot of ram
large: max heat and power, bit of ram tested
custom: specify settings - usualy i just put in half my RAM to use.
blend is the hardest on the system but hardest to pass i think
i run either small or blend