I've got almost exactly the same amount of land and do much of the same work on it that you have planned, GK. Most of my pine is 25-30 year old white pine. 30 to 40HP would be better and 40 to 50HP wouldn't be too big. I've got an old 50hp Ford 4000 that's been my mainstay until recently. That old gal sorta opened my eyes. What my smaller tractors struggled to do, it did easily. There was always power to spare.
In December I bought a new 45HP Kubota L4300DT with FEL. It's got plenty of power but is quite light compared to the 4000. I've come to think of the L4300 as a 30HP tractor in size/weight but with a 45 HP engine. It remains to be seen how well this combination will work out. My concern at this point is not that I've gone too big, but that maybe I should've gone to a full sized utility tractor like the M4900 or bigger.
Anyway, for snow removal around the homestead this winter, the L4300's compact size is appreciated. It'll help mowing around the pines next year also. The old Ford 4000 is still on hand if muscle WITH weight is needed.
Keep in mind that you won't have to push a larger machine as hard to do the same amount of work; so it should last longer. Also you're ready when the occasional job comes along that a smaller machine just won't handle. The range of possibilities is greater with a larger machine (within limits).
50 acres is a lot. You need something more than a glorified lawn tractor. Seems like someone here told me that a year or so ago when I was considering a TC30 /forums/images/graemlins/grin.gif.
Bob