how would a Peavey Max 115 II 300W do with a 5 string?
Listen to CKY.
Well enough.

For headphone practice, though, I found an old Pod XT BASS (they made one!) that has a bunch of amp/cab sims from well-known bass amps.

Should be around $80 (used -- no longer made) for a bean like this one, a bit more for the floor or rack models.