Well to offer some not-so-technical advice, I have ridden my 421 cub everywhere. It's been on trails, dunes, dragstrip, riverbeds, you name it. I'm running shearers and 35pwk's now but haven't had much ride time on the 35's, still trying to tune them in. I've rode it with T-5's and 34pj's with 13/42 gearing and it ripped. Was it tuned down? Yeah. Do I feel alot more power with the Shearers, yeah. It has lost a little down low but with the 13/42 gearing I gained some of that back.
I recently switched to 14/41 gearing and haven't gotten to ride it hard because of some WOT bog issues but it definitely feels like it pulls higher and harder. I'm still not convinced on the gearing though because I can't launch in 2nd now which I love to do. Might go back to a 13 front and leave the 41 rear or maybe a 40 rear. I'll just have to play with it some to get exactly what I like.
Hope this helps ya. If I were you. Do your clean-up ports. Put on whatever setup you have and ride the damn thing. When you can get some mid-top end pipes throw 'em on.