I mean I'm a 3.5 and have had the opportunity to play with some college age ~4.5 level guys recently. When we're 'just hitting,' I can keep up somewhat and at least rally with them (with less consistency or pace than they have, but at least it's a rally).
But on the occasions we've played sets, I try my best but it's just hard to keep up. I'd love to hit dipping crosscourt returns off of 4.5 level serves at will, but it doesn't happen very often. My first serve isn't bad for a 3.5, but it seldom seems to trouble these guys either. My best shots only rarely give them serious trouble (especially given that they don't often give me something that's easy to attack), meanwhile their rally-ball has more pace and spin on it than I'm used to seeing.
So yeah, if the gap is that big, just try your best on each shot. Keep hustling. Try not to get frustrated, and take your beating with dignity.