I think you are doing the right thing by testing the size you will eventually want to move to, especially while on stick height. A lift doesn't buy you clearance, it just buys you time till you run your tire into the truck. Unless you are extending the bumpstops (and timbren bumps don't do that), being on stock height is a great why to already test what will eventually be some amount of compression. So carry on brother!
This is also probably a good time to talk about suspension, namely ironman suspension. Here is a very new review from Andrew White, a man who has tested more suspensions than all of us and all of the vendors in this forum combined. And for what's it's worth, which isn't much, I completely agree with everything he says, starting at 12:40.