Huge difference from the 128...my buddy is no where near as tired at the end of a day as he was last year ...It will still trench if you going slower, but not so bad if you're wide open in the powder. I got the kit from my Arctic Cat dealer - my kit was a 128 - 151, I'm not sure if they have one for hte 144 - 151 and I'm running a 1.5 lug.
The 151" looks good on your firecat.
I just got back from Northern Colorado (Rabbit Ears) and needed a longer track. We had fun, but got stuck a half a dozen times. Getting stuck at that elevation in a killer with such little oxygen.
Last year I rode my buddies M7 144, and it is a totally different experience. Wish I could afford one
What did the kit cost, and how long did it take you to install?
Right now the weights, springs and helix are all stock...the only adjustment was to tighten the secondary by one notch as max RPM had drpped to 7700...now back up to 7850 - 7900. I am considering an ODS clutch kit, but need to find out from ODS Dan if I will need heavier weights/springs than the standard kit provides. My buddy has a 151 FC too and he was running 76 gram weights in the primary and I would have to check with him on the springs (I know he has stiffer than mine).
The kit cost $199.00 Canadian from the Arcticcat dealer (marked down from list of $1000 - I think). Then the track cost about $800.00. My buddy and I picked away on it over the summer, but it probably took somewhere around 30 hours...but we could probably do it in 16hrs now that we've done it once. It's really not that complicated.
I had one before I got my M a 03 F7sp 151X2.0. It works alot better then a 128 but still has the problem that when you run out of momentum you dig down but you don't loose momentum as easy. Run a 51 or 49 degree flat helix for better backshift and better belt grip. Cats suggestion on weights work good and the stock springs work great. Suck the limiter strap up for better approach angle and drop brackets will help to. Chop the snowflap off at the bend. As far as the track goes its alot cheaper to go buy a generic 151X15X2.0 2.52 pitch track of which there is alot of good useds ones around and cut it down to a 13.5 thats what I did. A couple TPI valves on the airbox help to when the beak plugs up with snow. Hope that helps.