You're focusing on the wrong end of the tractor IMHO. The transmission is the weak link in any lawn tractor. Deere tractors have 3 levels of transaxles: K46, K58, K72. All are made by Tuff Torq in Tennessee. Because the tractors all look similar in size, buyers tend to overlook the transaxle.
The K46 is a non-rebuildable, non-serviceable, sealed for life (can't change oil) lawn tractor tranny (think L series and X300/X350). It has a 3/4" axle, no charge pump, and is designed for no bigger than 20" tire (some tractor brands mate the K46 with way too big of tire). Tractor weight, tire size, and usage determines its life. If you're an average size guy, have no hills, and don't pull anything heavy... you'll get about 350 hrs of trouble free service (35 hrs / year for 10 years is the design life). Your mileage may vary.
The k58 is serviceable and is a decent step up. It has a 1" axle and a charge pump so is commonly mated to 22" tires. The unit is designed to change trans oil (some here have figured out how to service k46 though).... huge dealy if you want the unit to last. Deere X380 has a K58. If you plan to pull anything, mow on hills, or just a big guy... I wouldn't go under a K58.
Deere puts the K72 into all of the X5 series tractors... a garden tractor actually. The K72 is a beast: 1" axle, charge pump, diff-lock, and completely rebuildable. You can pull a plow with these things and put on high hours... just need to change the trans oil. The weakness in these is the input sheave/shaft joint... they will 'fret' and strip the input sheave splines @ 350 hrs if not taken apart, cleaned, and greased every 100-200 hrs.
I have hills and mow with an older GX335 because of the K71 transaxle. They are beasts! Just change the transaxle oil and grease the input sheave splines every 200 hrs and she'll out-live you. Hope this helps!