4 seat every time
The extra seats well worth the extra money for me.
I think a serious investigation into diesel engines would be worthwhile. Lower fuel flow, great torque spread, and the later gen engines are much lighter than previous ones - twin turbo units easily producing 300shp, which is equivalent to the RR turbine in the R66.
I believe RHC have already installed a diesel unit into an R44.
As a petrolhead, I'm always amazed by how low-tech the Lycomings are compared to the automotive market offerings, and think even with petrol engines, there are some huge gains in power and torque vs mass to be made. This change in itself would dramatically increase the envelope of operations for a machine like those you've suggested.