I have 5,7 m rib and merc 60 efi 4 stroke on it. 4 adults on board 18 knots at 4500 rpm 24 knots WOT. It is economic, 90 hp would be beter but 90 hp outboard is double price than 60 hp. Most of time it is 2 divers onboard and for that it is ok. Previus engine was evinrude 115 hp ficht and on 4000 rpm cruising speed was 23 knots but 20 l/h nov 19-20 knots on 4500 rpm and 10-11 l/h whit 60 hp merc.
I run an SR4.7 with a 50EFi Merc and it'll do 32-33kts with 2 on board. The 4.7 has exactly the same hull profile as the 5.4, so is essentially the same boat, but with a 700mm section chopped out of the hull, deck & tubes!
Make of that what you will, for comparison purposes.