I have a 50km long, 450m elev gain round-trip commute. I've ridden it on 3 different bikes, 2 using the same powermeter pedals. Unless you "upgrade" to a TT bike, a nicer bike with no other changes will save you maybe 5 minutes, and that's being extremely generous. There will be a bigger difference from having a strong headwind vs. tailwind and from your energy levels on a given day.
I should mention that my times dramatically improved more from the consistent training benefit of commute cycling after a year, about 10 minutes shaved off. If saving for a really nice bike gets you more motivated to ride, then that will also make a much bigger difference than the aero and weight savings.