For hard and elite dr silver and good bosses yes it's better to use a min II or crafted combo and for these khopesh would be better than rapier.
I personally don't value boss dps as highly as I did before. I run almost exclusively epic content and the only thing in there that requires a dr good and silver combo is epic DA. Lailat requires dr good and cold iron but a min II or crafted rapier with smallblade offhand will outdo most anything other than dual crafted khopesh as she has fairly low dr and no fort. Sure theres the occasional shroud or tod run but dual +4 holy burst silver rapiers of greater lawful outsider bane are just fine.
For boss fights also the gap between rapier and khopesh for me is made up by the fact that I can take rog past life feat instead of khopesh which provides more dps for up to 3 minutes.