The 40's will make better HP & torque across the board, while the P's will make better peak power. I'd go with the straight 40's, & grind out the EGR bump.
you will make about 20-30 more h.p. with the "P" heads on top end, but the regular 40's will have better low end torque. i run a 85gt, 306, gt40p's(box stock),b303, weiand single plane and a 650 holley and run constant 13.0's @107 mph. i say go with the "p" head, you want power right...?
forgot to mention the combustion chamber in the p's are smaller (58cc's) so they will yeild higher compression approx. 9.5 to 1(more power !!). i also run the new motorsport headers, they fit and look awsome, nice stuff but pricey.
i bought a set of GT40's with 1.7 RR's, i did a 3 angle valve grind and cleaned em up, now they're at a local "engine master"(kind of a family friend) getting fully ported. This is for a 351w i'm building, should make 350+ HP if i'm lucky, i say go with the regular 40's just because you supposedly can gain more in the port work than the p's, and get the same or higher compression with the right pistons(flattop should be 9.5:1 easy with the regular 40's), i have a set of BBK chrome shorty's that should fit the P's for sale, and good luck with your build, either way you cant go wrong!