During my build I looked at the XP cam from ZZP and the S1X from Intense. Being on stock heads like yourself clearance is important. You will want to change your valve seals and springs to support your decision.
My suggestion to you is to talk to many people that have ZZP cams and Intense cams. Listen to them unbiasedly regarding which "makes more power" and interpret hard factual track numbers on similar setups to what you plan.
Both companies appear to have good cams for many applications. Both cost the same. The only real thing is..which one will be able to make more of what you are looking for with your other mods.
BTW..3" won't be necessary and may only help in removing some low end torque.
00 Regal GS: All kinds of cool stuff.