I just put the plates on my car and I highly recommend them. I haven't dyno'd since I installed them a couple weeks ago, but low end power is definitely INCREASED.
Those plates aren't there to control tumble velocity and low end power like the imrc plates on the 96/97 Cobras. These cmrc plates are here for emissions and emissions only.
They may only show slightly less than 10 rwhp, but you will see that across the entire rpm range. Personally i think people get too hung up on dyno #'s as well. They WORK at the TRACK. With the factory cmrc's, my car would bog when I powershifted to 3rd gear. I personally believe the cmrc's close between shifts and that is what caused my bog.
I went to the track last Friday with the cmrc deletes and the bog was gone completely. I gained 1 whole mph in the 1/8. The weather conditions were very similar between trips to the track as well.
They are VERY easy to install. I installed mine and reflashed my computer in under 1 hour. The intakes are incredibly easy to remove on these cars.
They aren't THAT expensive either. PHP's can be had brand new for $200 and the billet Steeda plates brand new for $300. But if you search the classifieds you can find them used for cheaper. I paid $200 shipped for my used Steeda plates.
If you have a "custom" tune, you can get a cmrc delete tune from somebody like BamaChips, Brenspeed, or Evolution. Yesterday I installed my new BamaChips tune, we'll see how it turns out.
If you have a canned SCT tune, there is an option in that tune for cmrc deletes. I called SCT to verify and that option DOES INDEED install new spark/fuel tables; it does not simply turn off the check engine light. I had the canned SCT tune and ran mine at the track with the cmrc delete option and picked up that 1 mph.
I see only ONE negative with them. They are obviously there for emissions. Without the plates, the car seemed a TAD bit more "smelly" to me at idle. It's not that bad at all, but I can tell a slight difference at IDLE. Granted this was with the canned SCT cmrc delete tune. I haven't had the BamaChips tune in long enough to be able to notice.
I say do it.