well if I were you, and I'm not, I'd really look in to a good, used belt drive WB and get a velke for it. Save up and pay cash. If you're doing 4 lawns per hour with a 21" pusher, you outta triple it with a 36" or 48" WB. If you can stand on a wheel and let it pull you around, you can go in 5th gear and fly. No matter what you use, you outta be getting more than 11 bucks a yard tho. 44/hr might seem like good $, but if you charge even $15/yard, that jumps to 60/hr. If you can be more productive, you can do more yards in the same amt of time. So say even if you double productivity with a bigger mower, you're now at 8 yards per hour @15 per yard. Now you're at 120/hr minus the cost of the mower, fuel, and of course INSURANCE, LICENSING & TAXES. But I'm sure those last 3 aren't an issue.
if u don't have insurance, you can find a cheap 1 mil policy for about 500 bucks a year. post back and let us know what u decide.