I have not seen the figures you quote in real life on 340s I have flown? The five is turbocharged intercooled and wastegated.
I have talked to 340A pilots who have seen those numbers. It's not surprising - the Seneca has 10.8 lbs/HP, the 340A has 9.7 lbs/HP.
The RAM 340s are also turbocharged, intercooled and wastegated.
I don't think you're going to convince me the Seneca outperforms a 340 in climb or cruise. There are other reasons one might choose a Seneca over a 340, but those aren't two of them.