The OP states he has a L3301 so 27.7 advertised PTO HP. not a L3901. So not really a bad match up for the 42" tiller although it should handle a slightly larger tiller. Besides size of tractor has nothing to do with ground speed which seems to be his inquiry.
I have a RTA1550 and it works equally well on my L225 or my L4310, But I would not try to till acres upon acres of land with it even if I had a wider tiller. In that case I would plow and fit the land before I tilled it.
A respectfull word from experience.... and age...
I tilled medium and large grandma's gardens in the 1970's. I tilled large lots and acres of land for commercial lots.
All in the 1970's and 1980's. All with a Kubota B7100, which is 16 HP. And a 48" PTO rototiller.
If it was a small garden, say 20 feet by 20 feet. ( OPs situation). I passed on bidding the job. That is too small for a tractor. To fully get results you need a walk behind tiller.
The L3301 and L3901 are the same sized tractor. HP is different, but not much else. The model number was a mistake on my part.
Bottom line is I have experience rototilling for myself, my family, and commercially over decades. If 1980 in your forum moniker is your age, well I was tilling with Kubotas before you were born.
If so, I have kids your age now and they think, even at 40 y/o, that they know Everything.
They don't, and I don't know everything.
The difference is that I would not argue with my Dad about what he knew. He lived it, I didn't. I had respect for lived experience. Young folks these days are Hi and Mighty. Not respectful or intelligent in things that they have no experience with.
I know some things very well. And tractor PTO rototillling is something I know. I lived it as a job for decades.
You can probably fix my computer or tell me how to install an app. Thank you. I sometimes need that.
But to suggest that I don't know something that I lived through. Lol. That's what my 40 y/o kids do.