Grew up with the All-Stars version, have heard that SMB1 plays MUCH better on NES re speedrunning - is there a similar discrepancy in SMB2 or any other significant differences to be aware of?

I had some issues getting used to the original version after solely running SNES; mostly due to not having two run buttons and slowdown from lag. Other than that, you could easily relearn all the strats and use your knowledge of general movement to transition your skill over.

You cannot double jump on all-stars, nor can you do the veggie glitch. Aside from that, movement feels a little different, but they're very similar. I always feel like the nes version is slightly more responsive. On All-Stars you can super-jump while holding onto an item (Like Luigi in 1-2 with the key), while the nes version would require a pause. If you play either a lot, you'll get adjusted without much issue