Not a bad production rate for logs... I had a C32(1125HP) powered 6600 for awhile, and with full trees on a land clearing job we got over 500 yards an hour, but averaged about 350-400 over the total job. With just wood in the yard I was getting around 200-250 yards an hour. In the heaviest grinding I saw fuel consumption rates of 65+ gallons an hour. We ended up purchasing a 4600XL machine that will be here this week. Was a repo unit out of SC. Little smaller mill, and power(C27, 870HP) but should do just fine until we replace our tub with another horizontal(within the year is the plan).
If you have a deal set up with someone for use of a grinder I would ride that out for as long as you can. The maintenance on these things is huge, and only goes up with HP and hours.