In my opinion, go for the big bore. I've got an 05 M7 with speedwerx 800, full Speedwerx exhaust, boondocker, V-forces, sno pro intake, KOSO egt's, rear float conversion, 141" etc etc. The big bore setup in mine is awesome. Will outrun a 09 1000 in a drag by 2-3 lengths and fels way more peppy on the bottom end than the 1000. Only drawback I've found with mine is it's thirsty for an 800, gets a little bit worse mileage than a 1000 been drove hard. But lots of power so you give up some to get some if ya know what I'm saying. So far 1200 miles on it and pistons look good. Gonna try the 10.4 conversion next year and see if it helps too. All said and done I've only got $7500 CDN into my sled that will outperform an brand new one at $14000 CDN (for a X-Fire 1000 Sno Pro, and I know I know the X-Fire will outrun me on the topend but it takes over a quarter mile before he catches up)