I can not give you any info on the 44-48" mowers but I personally have a 13 HP 32", Gravely ProG, and I LOVE IT. My dealer is AWESOME, and thier warranty is tops.
Here is my story:
I had my mower for about 2 months, and only put on about 20 hours. After about 4 hours of cutting, the mower would start to whistle. It would never do this until the last property of the day, no matter where it was. So, I brought it in, and they said that the transmission was damaged, and they changed it. AWESOME. Well, about two weeks later, the noise started again, so I brought it again. They looked at it, and they noticed that the main (if i remember correctly) drive belt was not tightened, so as the day progressed, the belt would loosen, and whistle. They fixed that in 30 minutes and I have not had any MAJOR problems (knock on wood) in the first year that I have had it.
I love my gravely, and am looking if i get enough business to get the PM 252 or 260 Z.