The KAWI motors have always had the power... I love the uumph the T-rex has - BUT - that thing is HUGE! I dont know how some make it through some of the tight sections at a race...much less at race speeds... its just a bus IMO... but put that engine or Arctic Cat 1000 in a rhino or rzr and you might be onto something... of course though, if you are going to the trouble to do a swap, might as wel go ROTAX or something equal..
all in all though - they are nice machines - and it would be my next choice behind a rhino, only because YAMI hasnt released a 1000cc model, and KAWI isnt Polaris or Arctic Crap.