your gonna get a few opinions on this but heres mine. i've had three 800's and if i were to get either the 600 or 800 again, it would be the 600sdi. the sdi's sip oil and get incredible mileage. and imo have damn near the performance of the 800. i've had one complaint since the introduction of the series III 800 and that is its not strong enough for an 800. don't get me wrong, they run great, have great torque and all of mine have been mechanically bulletproof, but a good running 600 sdi will hang right with (or rarely even beat) a 800 all the way through the powerband. i've seen it too many times to think otherwise. so, until they come out with a 150 hp 800 sdi, it would be 600 sdi for me out of the two choices. :div20: