755inNY,
Yes, the 4210/4310/4410 are very similar in size and the 4310/4410 are nearly identical. However, the 4210 weighs in at around 2675 lbs as opposed to the 4310/4410 that weigh in around 2900 lbs. For the sake of grouping, the 4210 seemed to be closer to the TC29D/TC33D (2500 lbs) in terms of weight. The 4310/4410 seem to be more in line with the Kubota L3X30 series (3300lbs) and TC35D (3250 lbs).
It's one of the reasons why I like the TC33D. You get 27HP PTO in a 2500lb tractor as opposed to the L3430 (27HP PTO, 3300lbs) or the 4310/4410 (25HP/28HP PTO, 2900lbs). You are getting the power but not the extra 400-800lbs of weight, which I don't want for finish mowing. I realize the extra weight is typically desired for other applications but I will be mowing a majority of the time. It's also why my second choice might be the 4310/4410 over the L3X30 series. Similar PTO HP but 400lbs less tractor weight.
For that matter, I was originally afraid to make the move from the B7500/B7800 to the TC33D because of the extra 900lbs of weight. Moving from the TC33D to the TC35D would add another 800lbs of weight. A total of 1700lbs from where I originally started.
Of course, all of that is assuming everyone weighs there tractors in similar fashions! Probably a big assumption.