I put in the Mach 5s a couple of weeks ago and couldn't be happier with them so far. Mileage doesn't seem to have dropped much if any over the 1. 6s and I can still drive the truck without smoke. An HTB2 charger is keeping things cool as well.
Feel free to PM me your phone number and I'll go over more specifics with you. I hate typing on this keyboard.
Another vote for Olee Poole. He's excellent to deal with.