I get 5mpg with the nh250 even towing another 939series.
7-12mpg out of various A2's in varying circumstances.
More power right off the line with the nh250, and they shift better.
8.3 pulls hills considerably better, and tows heavy loads better. Example - M923A2 towed a 16,000lb mk16 uphill at 35mph on the way back from Nellis AFB. Loaded M925A1 was reduced to a 15mph crawl on the same hill.
Purely subjective, but I really like the sound of the NH250.
Great experience of both above without having to buy either! Yes, 250 sounds like a semi truck, 8.3 sounds like a school bus (because they both really are).
I bought mine from a member here, tractors0130. I'd recommend anybody to buy from him. He had it in tip-top shape when he sold it. I was very glad to pay him more than auction price for the work he did, the time and trust he allowed when I was looking at it, and his honesty. Doing so you will pay several thousand more than auction price, but it removes most all the risk because you can spend some time with it and test drive it. Auction can say "runs" but doesn't say it has a hole in the engine block. Auction can also say "won't start", and it just means dead batteries. Or, anything in between. 923's have sold for less than scrap price at auction, and driven home. If you really want an A2 with all the tricks, needs nothing, and minimal risk, you'll pay up to 4x or so as compared to an auction one that is pictured with flat tires. Add-on's can be pricy. Cargo cover alone can be expensive. Then you need the bows to support it. Converting a non-winch truck to winch can be expensive and a lot of work. Used parts alone to do so are in the upward neighborhood of $2000 or so, and you still have to do the work.