CC,
Thanks!! While there are lots of variables, the 4155 will run a bigger hog and cut heavy brush better. I think you would definitely notice the 15hp difference even though they are both the same basic size and weight.
What I think you would notice even more is how much smoother and quieter the 4100 series 3 cylinder turbo is versus the 4000 series non turbo 4 cylinder. I sat in both cabbed machines and ran the motor at about 2200 rpms after everything was warmed up. The 4100 series was much, much quieter, enough so that a phone conversation would be easy. In the 4040, not so much. If you are at elevation the turbo motor will maintain power better.
Price wise from what I have seen the $20K 4040 seems like a decent deal. I think the 4040 is about $22k around here. For the $6k more you are getting the newer 4100 series, 15 more hp, and 50hr regen instead of 5hr or so. I think a big part of that price is the 15hp. Maybe a good compromise would be a 4140?