what are the performances differences between these two intakes?

For what it's worth I installed a Performer RPM intake in place of my stock 1985 GT intake and went from a best 1/4 mile mph of 95.89 to 98.51. That's about a 20 flywheel hp gain. I also didn't notice much, if any, loss in low end power/torque. And that's with the intake that makes power from 1500-6500 rpm....the intake you're thinking of is idle-5500 rpm.

May not be what you are wanting to hear, but I like the Weiand stealth much better than the two listed.