After driving a few cars with both cams i would say the S1x is a far better cam, especially cars with stock gearing. Peak HP numbers mean nothing when you have very little power below 3500. Boost bleed off is to much with an XP. Both work with stock heads just fine as long you use #105 springs and aftermarket retainers. If using nitrous or 3.29-3.69 gears then the XP seems to be a better choice depending on a few other factors. Most people have to run a 3.0 pulley just to get 10-11 PSI with the XP.....its not optimal to have to spin a blower that fast for those boost levels. A headers primary size also play a big part of where torque and peak power will be.
Ron vogel made a chart with all of the 1/4mile times and which cam works best with differant gearing.
Dont worry about what RPM the blower is still able to make power till. Its the horrible high RPM breathing design of the series II that will hold you back. its just not ment to rev that high...no matter what cam or heads you have. If you want to rev high get a series I.
