I almost sure that 3,4-mdpbp will be just as good as mdpv is, but slightly weaker of course....it nothing changes actually, unless you have huge tolerance, both should be very strong... I was just(for some time....about 2 years or so) comparing *pvp and *pbp "families"(in fact I've also tried buphedrone/4-MBP/3,4-DiMe-buphedrone and pentedrone + 4Mpd...buphedrones certainly are closer to MCAT's by effects).
3,4-md(ohh....this magic MD..)pbp I didn't tried though.... But used all kinds of pvps through very many years: used periodically with little dosages, lets say 1g for a few days. Used everyday(up to 1-2g a day).
MDPV is my favorite drug by the way, not only here but from anything I've tried, it's just perfect for me. I mean hq stuff! Low quality pyrovalerones, and derivatives are acting not as they should, you may get almost opposite effects from it.( It's not comparable at all in many cases! ) .
So... After many years on pvp's, or even more(sometimes much more) potent analogs I didn't waited too much from pbps... Even having in mind that a-ppp compared to apvp turned out to be not that weak as I expected, though 4meppp is shit.).
I used quite for some time pbps, mostly 4-me,
now I'm back again on PV....

both are very very strong and similar by effects! Not as shitty and crazy as unsubstituted ones certainly (up to 1 moment I didn't understand before how anybody can like it!!! Now I somewhat understand it. But prefer not to touch it.. and it smells worse than any other
3,4 Mdphp could be intresting compound, may be I already tried it before, idk... other phps of course shitty poisons, in my opinion(mostly shitty!!! And a bit! a bit poisonous....))))
PS: btw I'm smoking now PV + 3,4-DiMe-Buphedrone combo...(fb of course!))) Oohh it feels much better than pv by itself Im sure... But few days were spent in almost uncontrollable delirium, always promise to myself not to let it happens - never again!!! but sometimes it runs out of control...
With Mdpv I never had such problems, never!!!