the 105s gas and diesel both used the same engine as a gas and diesel 4020. Fuel consumption would be similar to the tractors at load.
Our 105 diesel never has any power issues, and will handle 250 bushel irrigated corn with the 6 row head... no b.s! The issue is you can walk it over the back, slip the cylinder belt or run out of clean grain elevator capacity long before power. Ours is gear drive.
The biggest issue is the cylinder belt. the variable speed cylinder was only offered the last 2 years or so, and I don't think really perfected. I'm not sure, but I think it's the same drive that the 55 and 95 used, just with a bigger cylinder and engine on each side of the belt!
As for fuel consumption, it will run all day on a tank.
I must admit I feel a little empty writing this. We did buy a 9500 to replace her this fall, and she's still here (in the shed!). We bought her in 1989 and used it til this fall. Trying to do 250 acres with it though is getting to be too much, and some parts are darned hard to find.
She's a good friend though.