Chariot is the way to go. I run the ultra high flow full kit. Here is some options for ya: http://motors.shop.ebay.com/i.html?_from=R40&_trksid=p3841.m570.l1313&_nkw=Chariot+banshee+impeller&_sacat=
I've ran a gear from Mull for about 1 year with no issues. Mull's quality is top notch, I've talked to Brandon a few times on the phone and the guy knows his stuff.
I've seen too many plastic gears fail to even consider running one.
I've heard guys cutting the carb springs. Make sure the springs stay the same length.
There is a thread on exactly how to do it, use the search function i'm sure you'll find it.
I run right around 150psi or so. I havent checked it in awhile though. I'm running 19cc domes right now. At our elevation I know people even run 18's on pump. But I wanted to be on the safe side so I stuck with 19's.
6K-8K elevation, you would be fine running 18cc domes on pump gas. You may be able to get away with some 17cc domes at that elevation, just depends on your compression. IMO anything around 165psi and up should run race fuel.