How much money do you have to spend? I got a 08 m1000 for sale that pulls well..
I would look into at least a 600 liquid cooled machine from about 99' and up - 01 and up would be better. 144" track or longer would be best... I ride a 153" x 2 1/4 in track and it pulls just fine. Some of the super long tracks these days are overkill..
That 550 is a fan cooled machine and a liquid cooled machine will run much better for a skiing application... With that said the 550 will get you up a groomed or packed trail..
Also stay away from tripples.. The RMK's are not a bad machine. I like cats and the efi from 01 up.. Super simple they start on the 2nd or 3rd pull everytime. Cat started the with the m7 in 05 and that is a great start up machine that can be found for about $3500..
If the sled is super cheap buy her and if or when you want to upgrade you will have a 2nd sled for a friend...