yea of course 3 10w6''s are going to slam... A dude i used to know had the same setupd,,, 3 10w6's and 1500 watts and it was overkill.. But for 500 watts.. you mine as well keep the 12''s but do whatever your heart desires
Both given the same ammount of power running in the same type of enclosure, the 12's may have a slightly higher SPL. You have more area and air being displaced with a 12" woofer compared to 10".
The 10W6 however has more linear excursion capabilty. So it may even out.
The W6's will sound better no doubt. The 12W3v2's were the last subs produced by JL with out their patented DMA optimization. Only the 15W3 had/has it. And of course it doesn't have the superior W-cone of the W6 and new W3's.