I have the 2710, and the 2910 WAS available when I was looking. You already nailed the reason I didn't get the 2910 - the features didn't justify the price differential. Of course, after several months of price comparisons (just to be sure I got a good deal), I'm certain that I got a very good price on the 2710. The dealer was probably trying to move some, and didn't have any 2910s, because there was about a $2000 difference in price. The price quoted for the 2910 was on the high side of the acceptable range. I never use the cruise control, I rarely stall from lack of power (when I do, I doubt that 2 extra horses would have prevented the stall anyway), the seat/steering wheel fit fine as they are. The telescoping links would be really handy, but they sure aren't worth $2000.
With all of that said, I was originally looking at the 1700/2400 size, and I do mow. I followed the advice of everyone here - I went up to the largest size I thought would work for me. The L series was just too much for manuevering around my yard and between my X-mas tree rows.
As for Boondox comments on granite - The 27/29 may not be able to lift a full bucket of granite, but I've never had any trouble lifting and controlling a full bucket of rocks from 4" - 20" in size. I'm no geologist, but I think these are your basic igneous field rocks - not as dense as granite - but no lightweights either. You can do everything you described doing with a 2710 and not ever feel like you "settled". If you are going to dig out 800 - 1500 pound boulders, you will find the 27/29 a little lacking. I daresay, if that is all you are doing, you would find even a 3010 lacking. I have 10 acres - half xmas trees, 1/3 forest, remaining lawn, 800 ft gravel driveway, mostly level land with some mild grades. Its all I need.
PaulT