I ran my S10 system in that exact fashion. I used a PPI PCX440 (4x40). Channels 1 & 2 drove the Memphis 6.5 coaxials in the doors and channels 3 & 4 bridged to my JL 8w3 behind the seat (standard cab). It sounded AWESOME.

If you've got the money, check out the JL 450/4
http://www.jlaudio.com/amps/4504.html