It's a long winded reply, so here goes-
The 600 Ace is a better engine fuel wise, but I got the 550 at 4 grand less than the Ace, it's a pre owned 2013. I think the 550 gets compared to the Ace alot making it look bad on fuel but if i look at my Summit, the 550 should be quite reasonable.
Being the kind of guy I am, I disasemble my new Tundra as soon as I got it home. Installed a EGT gauge so I can monitor the engine, and just looked everything over. Easy to work on, no diff from any older sled, just you have to know how to take it apart, and I wanted to know that in my warm shop, not out on the line. Very basic engine design, plain old Mikuni carbs, no sensors to watch out for.
No dealer needed as far as I'm concerned.
Performance wise in deep 3' snow, was very impressed with low clutch engagement, 2500rpm and low gearing with a torquey engine.
Can stop and start where the Summit would struggle due to no track spin on the Tundra. Pin it on hardpack and it will pick up the ski's.
Good flotation on the ski's, and very nimble making new trails through the forest. Longer seat on the lastest Tundra's allows a passenger.
Headlight is way better then the older sleds, and suspension is better than I expected.
Only regret is not buying it at the start of the season.
Now with two Tundra's, my wife says she is coming along on the trapline line.......
I wonder who gets the new machine?......