2000 225 Promax Gearcase

I broke a pinion gear in my 1.75 TM gearcase and it took out everything but the housing. Approx cost to rebuild $2700. Complete new gearcase approx $3600. Last year when I had it problems with the clutch dog, my mech let me borrow a standard 2.5 gearcase until he could get my TM back up and running. I saw no appreciable difference in speeds, performance, etc.
Looks like I can get a standard 2.5 gearcase complete with warranty for under 1K. What's the real difference between these 2 gearcases?

I'm not a racer, 2000 Bullet 21XDC running a Powertech TRO4 at 6400 RPM max. I guide out of this rig about 75 days a year. Very seldom run hard or fast due to fuel prices, clients nervousness, etc.

Help !!!