Request Repower/reprop Advise 39' Sea Ray Express

[richard iappini]

I have a 1988 39' Sea Ray powered with twin 454/340h.p. Mercruisers with 1.88:1 gears turning 18"x16.76" props; max rpm = 4500 . The boat cruises at 3300= 16-17.5 knts W/full fuel. I would like to get a faster cruise speed 19-20 knts. Would 2.5:1 gears help/hurt my cruise with new larger diameter props? I may be able to add 2" of pitch to increase my cruise a knot or 2 to my cruise as is? Second, if I repower would new 8.1 Mercs or Crusader will they produce enough power to raise my cruise to 19-20 knts? The new engines produce approximately 65 ft.lbs more of torque each @ 3200 compared to the 454 and should burn less fuel. Has anyone repowered with the new 8.1 engines and what type of increased performence did you see compared to the 454's - both speed & fuel burn?