I just bought a 99 vermeer 1800 with the 115hp John Deer and it works great. The autofeed only kicks on when you're working it real hard and then, it does its job by slowing down/stopping the infeed wheels so the engine can build back up. I've owned two of this year and model now - one back in 99 when I bought it new and used it for both residential and reclamation/land clearing work and now the one I just bought a month ago and use solely for residential tree work. Even for land clearing, the 115hp engine seems to keep up with a bobcat feeding it big stuff. Now, if you are planning to have several bobcats feeding it as fast as they can, you might wish you had a bigger engine so the autofeed wouldn't kick on so much but, for the average user, the 115hp works fine IMO.
That said, the only problem I have with this engine is when the final chunk of a tree trunk gets fed in. When the trunk section gets behind the feed rollers and they cannot reverse it back out away from the drum, the engine will pull down significantly on large wood. I have stalled the engine a couple of times when I wasn't at the feed bar to slow down the feed and let the engine rev up to full rpms before feeding in the last 12" or so of trunk wood. Only in this case would I wish I had more hp so that the final little chunk wouldn't pull the engine down so much.
It's a good chipper and I'd agree with ASDs comments about it outperforming a 12" chipper 2 to 1, however, I have never run an 18" vermeer against a bandit 1890 so I can't comment on that but you can assume that most any chipper with double the hp will outperform the smaller engine.
