I had the same idea about accuracy and underlevers, and when it came down to it I just found the underlever a bit easier to cock, but less fun to load. Probably just a personal preference. Don't let me talk you out of it. My TF97 feels like a toy against the TF87...87 is a good 8 inches longer. If you are interested in an underlever, I think that is the one I'd be buying now. Really I'm debating keeping it...but the rifles are mounting up.
I am that guy whose gun went out same day, and the tuned gun is totally awesome. I'd already planned to send Gene my next gun which I thought was going to be the TF87 in .22 with gasram...but now that it turns out the TF87 is an underlever, I'm jumping to the next project and combining the two guns I had in mind: a TF89 in .22 with gasram, custom stock and muzzlebrake. As I'm getting one gun instead of 2 (even just buying 2 guns and a tune for each would have been about $650), the budget for the custom gun can go up. I am so happy with the TF89 in .177 that I'm sure the TF89 in .22 will be a great starting point, and a really great rifle when all's done. I'm figuring about 2 months if all goes well. I wish I'd been ready two weeks ago when the TF89 went on sale for $134. It's only about $15 more now, so it hardly matters in the overall scheme, but I like to get a good deal.
According to the results, the extreme difference in the tuned gun was 15 fps over 10 shots, with only about 3.5 fps ave. That is down from 40 and 11. I had wanted to swap out the trigger, but Gene told me I didn't have to and tuned the one that was on it. It is a new world and he saved me a few bucks here and there. With tune, for about $300, I have an awesome rifle that I'd stack against just about anything. Except the one I'm going to put together as the .22 should be more efficient and probably more accurate than the .177 with more striking power.