It will run a Yanmar 4 ft tiller fine. I have a Yanmar RS1400 tiller, the tiller that was factory-equipped on YM2000. Its 1400mm, (I think 54") wide. That works the YM186D pretty hard but its usable. I'm using it to clean up where the big disc behind a 70 hp tractor couldn't fit. However - if I'm tilling along in disced ground and have to step up onto undisturbed ground like climbing a stair, then as the tractor nose climbs, the tiller gets forced in deeper and this can stall me.
I don't know if a rental tiller (Howard etc) works a tractor harder than the Yanmar tillers that were designed for rice paddies.
I think for a simple vegetable garden a 4 ft rental tiller would work fine. Worst case, you might have to make a shallow cut to break up the turf then a deeper second pass. Don't be afraid to run the tractor hard. That's what it is designed for.