I have been researching the AFE CAIs also. The high breather will make less HP/torque than the lower model. The lower model gets rid of the stock air resonator. Since I live in the snow capitol of the East (Upstate NY), I think I'm going to go with the high breather so as not to suck any snow/slush into the lower one.

 

Just wanted to say that I'm using the AFE High-Breather and Magnaflow 1-2 Dual setup. I'm very happy, but since I did both at the same time, I cannot attribute performance gains with one over the other. Other than sounding great (if you're curious Magnaflow's site has video clips that are pretty accurate) I chose the high-breather due to the fact that I like the that the resonator says "HEMI" on it.

The AFE also seems to have the largest filter over other CAIs and the heat shield is a plus. You cannot deny that it is much easier for air to get into the throttle body (or at least the resonator) based on the design. Although I have no metrics to prove it myself, I can say that the combo did noticeably improve acceleration. How much it saved in MPG is more of selling point used for the wife to approve the purchase.

2004 QC 4X4 1500
SuperChips
AFE High-Breather
Magnaflow duals
Motive 4.56 x 2 (4x4)
Toyo Proxies ST 305/50/20
Hawk LTS Pads
PowerSlot Rotors
Everything else is cosmetic