Well I've been using my new 2320 for almost two weeks now, and so far it's everything I hoped it would be. Feels more stable on the slopes than I thought it would, and I like the ability to slow to a crawl with the HST and back to speed so easily. Of course I upgraded from a manual shift with a stick throttle lever! The 2320 does not seem underpowered to me on the hills while running in low range- but high range won't handle the slopes. I cut and run it in low range for almost everything anyway. The 670 has an even smaller engine, although the low end torque is a little better- it will really go low range whereas the 2320 low seems to be a higher gear speed. And yes, the 2320 high range will really scoot! Wish I had the terrain and acreage to really use it... 
The loader works very well, and is easy to remove. I've heeded the advice to make sure to use a level hard surface for the stand. I've already moved some chipped wood piles, logs, mud, etc. Lifted out a small stump that I couldn't pull out last year. I have the 53 inch bucket to stay a little smaller and work in narrow places. But I can see the advantage of a 61 inch when paralleling a border... the bucket is then wider than the wheels, and can scoop or scrap more closely than a 53 because the wheels are too close to the same border. But I still think I like the smaller form factor... I won't be moving enough soil or gravel to make a difference. I need to get a toothbar... forgot about that! The tiller does well so far, but I've only used it to till the top 3 inches or so until it dries out a little more. Finally used the mower deck for almost 3 hours today and it works wonderfully. Like one of the other posters mentioned, I raised the "anti-scalp" wheels higher than normal and just put the suspended deck in the position I want. Sometimes have a lower cut on the down slope side, but that's fine. By the way, my old 670 deck would dig in the grass like some of the complaints for the 62D deck, but mostly when going in reverse. The wheels don't seem to pivot very well and can turn sideways in reverse, dragging the grass and dirt with it. I don't mow in reverse much, so it was never really a problem. Re. tractor size, I almost went with a 2305, but think the larger machine is a better choice for my property (10 acres), slopes and overall workload. The 2520 is not much larger than the 2320, but is a little higher with larger wheels... I would not want anything bigger, but I'm sure the extra power is always a plus. Something I really like is the more open deck of the 2320. Maybe I wouldn't notice it on the 2520, but my old 670 has a "hump" in the middle and I like the absence of that. All great machines- good luck!
The loader works very well, and is easy to remove. I've heeded the advice to make sure to use a level hard surface for the stand. I've already moved some chipped wood piles, logs, mud, etc. Lifted out a small stump that I couldn't pull out last year. I have the 53 inch bucket to stay a little smaller and work in narrow places. But I can see the advantage of a 61 inch when paralleling a border... the bucket is then wider than the wheels, and can scoop or scrap more closely than a 53 because the wheels are too close to the same border. But I still think I like the smaller form factor... I won't be moving enough soil or gravel to make a difference. I need to get a toothbar... forgot about that! The tiller does well so far, but I've only used it to till the top 3 inches or so until it dries out a little more. Finally used the mower deck for almost 3 hours today and it works wonderfully. Like one of the other posters mentioned, I raised the "anti-scalp" wheels higher than normal and just put the suspended deck in the position I want. Sometimes have a lower cut on the down slope side, but that's fine. By the way, my old 670 deck would dig in the grass like some of the complaints for the 62D deck, but mostly when going in reverse. The wheels don't seem to pivot very well and can turn sideways in reverse, dragging the grass and dirt with it. I don't mow in reverse much, so it was never really a problem. Re. tractor size, I almost went with a 2305, but think the larger machine is a better choice for my property (10 acres), slopes and overall workload. The 2520 is not much larger than the 2320, but is a little higher with larger wheels... I would not want anything bigger, but I'm sure the extra power is always a plus. Something I really like is the more open deck of the 2320. Maybe I wouldn't notice it on the 2520, but my old 670 has a "hump" in the middle and I like the absence of that. All great machines- good luck!