I have both these sleds
165 Summit X Turbo
154 Summit X Turbo
and also been riding the 154 Summit X Turbo 2.5
There are all super fun! The 165 is what i would have if I had one sled, super fun and it holds an edge better, suspension works better due to longer track and on the deep days, most of which I get all the time it is the machine to have. The said the 154 in both lug heights is amazing and will go every where but you will turn out more poach tracks to do it and it spins out more, some thing this is wash out but it is due to the shorter track. I can see why the expert would be more popular in 154 than 165 as well, I also think you are ringing the neck of the 154 in the deep which i get more of and its fun but you go through gas oil and belts faster for sure. All worth it for the fun factor. I am 145 5'7 so the 154 floats me fine but the 165 is so incredible in the deep snow. You can not go wrong with either and yes I think a 154 turbo will out doo a 165 N/A , the turbos are just so dam awesome! This was Tuesday March 5th and it has been like this for a week!
Factors
your weight - if over 200 pounds you are losing a lot of float. for example the 15 inch track on the freeride loses about 35-40 pounds of float-why guys complain of lynx and freeride trenching more if your not on it fast all the time
How much snow you get and what you like to ride. Deep Deep pow all the time 165 less of that half the time 154
do you like to adventure and get out of the busy places to further places...both will do it but again the bigger hills you push to get back the more you will be out of gas on 154 and the 165 will use less effort and gas to get there.
Ease on machine the 165 handles it all easier so easier on machine, the 154 is super fun but you got here matted so harder on machine...