I've seen the question "Why don't SpaceX just use Raptors in the F9 now since their better" asked here and there, and I understand why it isn't possible to do that- they're not a drop-in replacement and methane is stored differently and used in different ratios with LOX to RP1.
That having been said; if one ignores the fact that SpaceX is phasing out medium/heavy semi-reusable launch vehicles, consider if a vehicle were built in the basic form factor of the F9 (so 9 1st stage engines, and 1 vac optimised 2nd stage engine) from the ground up to accommodate raptors instead of merlins.
- What kind of performance could be expected from such a vehicle?
- And to expand further, if the need to use the F9 framework were completely relaxed, what would the optimum configuration be for a semi-reusable medium lift raptor-powered launch vehicle?