Same amp, just different speakers...and that amp cannot switch of its way to big bottom end
The 4x10 is very snappy and fast, the 2x12 is a little more like a twin.
4 10's give you a brighter tone with a tighter bottom end. 2 12's give you a darker more mid-range tone. Having had both, I much prefer 4 10's but it depends on which type of tones you prefer.
Yeah i agree with whats said above, and having said that i prefer the 2x12 because its tone is warmer and fatter to me than the 4x10. The 12" speakers just seem fatter to my ears, and thats what i love