All things (possible) being equal anyways...

Lets say 3100lb car, 4 speed, longtube headers and a VERY good exhaust system.

My original plan was a 67 383-2bbl longblock (not rebuilt), so lower "9.2:1" CR, Holley Street Dominator, Holly 750-800DP, MSD dist, no accessories, etc. Whiplash cam.

The option now is a mid-90's (or best year) 5.9L Magnum (unrebuilt), RPM Air-Gap, proper-sized Holley DP, elect. ign, no accessories, Whiplash magnum cam (to keep the comparison equal-ish).

Will the roller cam/better rockers and more modern heads make up for the 23cid and bigger everything? I'm sure it will kill the 383 in mileage. How about power?

I'm just talking about power here... bench racing... i realize the car would be generally faster (straight, top end, cornering) with the Magnum due to the weight difference.