We have a 2008 WD1203 with a 36' HB. The tractor has been good but we had a few problems with it this past year. We struggled with an overheating issue that turned out to be a faulty sender. By the time we figured it out and got the right part we were done swathing. We could only run at part throttle or the temp would start to climb into the red. Our other problem was a blown servo motor gasket on a wheel motor. It appeared to be improperly installed at the factory which caused it to fail. Patched it up with some silicone and it held up until we were finished. We have a few small but steep hills and it definitely lacks for hydraulic power here. I don't know if it's horsepower or not enough hydraulic pump but you have to slow right down when climbing because your reel and canvases slow down so much. Otherwise, on flat ground you can cut canola at 10 mph without too much trouble. If you make a mistake you can sure make a mess in a hurry though!
The HB header I do have some issues with. We've had an absolute b*tch of a time keeping the canvases aligned properly. I don't know if it's because I'm too stupid to figure it out or what but I just don't seem to be able to get them to track properly. I adjust them and they run fine for awhile and if I stop and check them a couple of hours later they are running against the top or bottom again. Part of the problem imho is that they make the canvases far too wide. I understand that they are trying to keep material from going underneath and wrapping but there is just no margin for error here. There's can't be much more than an 1/8 of an inch gap top and bottom when it's running centered. One neighbour had similar problems and their dealer put Macdon canvases on instead. We ended up ruining ours by the time we finished up.
As far as the JD's go I've never run one but there are several around home. From what I've heard the sight lines aren't that great, the first thing one neighbour did when he got his was pull the side mirrors off. I just can't believe JD is still using that same cab, it seems ancient now. I think the cab is definitely one bonus of the CNH power unit. They both seem to get the job done.
Sorry, that was a little long winded!