Discussed a 3320 vs 3520 in another thread. Anything I should know about a used 4510 as compared with these? I know it is a larger frame tractor similar to a 4120, but for the money (around $15k for an '02 w/ 700 hours) it might be worth it. It is a power reverser. With 30 or 40 acres to mow the bigger series might be useful..