My suggestion would be, if you’re gonna get a bmx, do it right and get 20″ wheels. If you’re thinking of 24″ then stop doing that and get a mtb jump/park bike with normal wheels.
In my experience* the size of the bmx frame doesn’t matter one bit. I rode the same sized bike as everyone else and i’m 6’5″. It had a layback seatpost and my bars were a couple of degrees further forward than most and of course i looked ridiculous but that didn’t matter.
I may have missed the different sized bmx thing that’s happened recently so can’t really comment on how a very long bmx rides, but not so long ago i was offered a spin on a rather special prototype frame at the local indoor bike park. The guy was maybe 5’9 and frame was tailor made for him to test (i don’t believe it was particularly long) and it was bloody ace. So light and easy to throw about but more interestingly, it rode like my old ‘one size fits all’ bikes.
So i’d further suggest that getting a bmx is the important thing and the fit doesn’t really matter. The only difference i can see having longer/bigger bmx is that it you’ll look 5% less ridiculous on it 😀
* bmx cv
i rode bmx vigorously from the age of twelve until my late twenties and more sedately for another eight years. During this period i undertook various cycling projects that included racing, street riding, dirt jumping and mini/half pipe as well as just riding about and doing skids.