When on the phone with him to order a 421 serval(my current build) a couple years ago, he brought up strait cut gears when i ordered my serval. I believe he said, for 10mils and up, he would recommend it. Like said, when you talk to him ask him. He will tell you the truth and not just try to make a sale.
Id like to know why you didnt want to go 10mil. I assume you talked to him and discuss that 421 will be all you need. For my weight and noobish riding skills, the 4mil making 70-80 to the tire was all i needed as well.
I'm interested in seeing CPI vs Snipers on that engine.