for what it's worth...
my sea craft,it's powered by merc 5.7MPI with the horizon package,bravo I drive - in my opinion,this is the best option,performance,and effciency wise.the boat gets over 2nmpg,cruises @23-24kts,and the engine runs up to it's 5000rpm limit,as it should.the engine has ran for 335 trouble free hours in the last 3 seasons.i've used these engines in numerous other repower projects,with,similar good results.
if you're not running a bravo drive,i suggest you purchase a package-"package" being engine,drive,transom plate-reason being-if you're equipped with an alphaI drive,the water pump in the alphaI drives,are,low volume,high pressure pumps,the newer vortec engines require a large volume of water,using the newer vortecs and the older drives,will cause a problem with the engine blowing head gaskets...
here's a recent trip i made on my rig -
http://www.facebook.com/#!/pages/spo...n/345108625395
we ran inexcess of 62nm to the fish,the engine was never shut down-fired up @ 4:30,shut down @ 3:30 total trip distance was 125-out and back,and running and difting...total fuel used was 52g...
that v6 is a reliable engine,very powefull,but,it just doesn't have the torque needed to shove that hull..