Lovin my diesel so far. I'd stay away from the 2011 diesels if possable, unless they've had the clutch upgrade. There was also a recall/upgrade for the air intake ducting under the floor on some 2011s. so far the 2012s seem problem free. Acceleration on the 2012s is improved as well because of clutching upgrades.
Top speed stock on mine was 40 mph. even with about 300 lbs in the bed. (test drove it at home before I bought it) but when I put the polaris pro steel cab on it I knocked my top speed down to about 34. at 200 hours I decided to fabb up my own turbocharger setup, and I've been running with that now for over 250 hours. 450 hours in total.
It's been used on our ranch on a daily basis for hard work, hauling, transport, hearding cattle, fencing, and about everything else a ranger can do, and even some things a ranger shouldn't do, but does anyway.
Only factory improvements I'd make on it would be making Nivomat shocks and power steering standard, and maybe putting a little larger diesel in it, like an 1100? it's tight in there with the 900, so I doubt we'll see it for awhile.