Hi Ken,
I have a PT422 with the Subaru engine. I've only had it for about a month now. We've used it some, but not steady by any means.
As far as the engine goes, no problems (though one shouldn't expect any this early). Texastomd is correct about there being more service centers for the Kohler engine, though.
I do not like the machine's layout for service. The engine's oil filter is hard (though not impossible) to get at, as is the hydraulic filter (though again, not impossible — just more difficult than it should be). Also, there is no shutoff valve between the fuel tank and the carburetor as Subaru recommends in their engine manual. The in-line fuel filter is a small plastic housed filter like you could buy at K-mart. I don't remember exactly how the Kohler engine sits in the frame, but I suspect it has the same "problems" based on the overall design/layout of the machine.
I also don't like Power Trac's "in-house" branded filters. There is no information on a cross to more common ones. You either have to guess and experiment or stock up on theirs. I haven't priced them yet, so I don't know how bad they'll be. I just know someday I'll need one and won't have one! And then I'll have to wait to get one shipped in.
Is it quiet? In a word, NO! But then, neither was the PT425 (Kohler engine) I used when we visited Power Trac. Actually, what appears to be a whining noise from the hydraulics is more bothersome than the engine noise. Since the exhaust is behind (and to the side of) the operator, it's not as annoying as you might think. Hearing protection is advised for either engine, in any case — especially if its used for any extended time frame.
Our setup is about the same as texastomd, except for the different engine and the 6" auger. (We got the optional canopy, arm rests, and bar tires as well.) We also got both buckets (smaller digging bucket with teeth and larger soft material handling bucket), 60" finish mower, 48" "brush-hog"-type mower, and the forks.
So far we've only used the mower and brush-hog, but I hope to try out the buckets in the next week or so. Forks will probably not be used for a month or so.
As far as the mowing goes, the finish mower works as well as our old Ariens and Cub Cadets did plus it allows us to mow more than they did since we can go places the others couldn't. The brush-hog also works quite well. We've cleared out a few small areas (a few hundred square feet at a time) just to test it out, but I've got some trees to cut down to open up a bit more to get where we want to end up. Probably sometime in the next two to three weeks we plan on brush-hogging a couple of acres of open field that have been allowed to grow up over the last five years. Some of the area is a bit "soupy", so it'll be a good test.
Anyway, just wanted to chime in with my two cents worth. Hope this is of some use.
Brent