<font color=blue> can it mow 5-6 acres many times every summer for twenty years</font color=blue>
When buying it is useful to consider what size implements you need to do your primary jobs, and then figure out what tractor can efficiently handle those implements. Mowing will clearly be your biggest ongoing need. With this much acreage to mow, I dont think you will be happy with a 4' mower after spending $15,000 on a tractor. If this is all finish mowing, you will want a 72" mower. If it is brushcutting, you dont want less than a 60" cutter.
A 2710 or 2910 will easily handle these size mowers and everything else you mention. I finish mow 3 acres with a 72" mmm and brush cut about 4 acres with a 60" medium duty shredder with a 2910. I wouldnt want to do it with smaller mowers or a smaller tractor. I could be wrong, but I have had the impression that GlueGuy doesnt do too much mowing on his mountaintop.
I'll leave it to others to comment on whether the 2410 or 7500 can handle these size mowers.