What’s the reason no one else bought the great deal on the 600?   Even if you buy the 600 thinking you can pass along to your son it sounds like in a year or so he is buying a faster sled.  So you better buy the 858 so you can keep up in a couple years.

This is spot on for what you guys are talking.  That said couple thoughts.   I hate trying to get in and out of North Bay.  Always seems to be a fight over mogul filled trails.  5 miles outside of town and things are great.  There is some resorts east of town you can try for accommodations or Mattawa is an option. I think you need to decide what side trips you want to do.  Coming up the west side Sand Lake is a good lunch stop and the ice caves near there are worth seeing once.  There is a big section of road running east of Powassan.  Like 10 plus kms.  If it’s cold and has snowed in the last week or two it’s no big deal.   When it’s bad it will kill the trip or make you detour west of Powassan for a long way.  In the north Bay Area you have the mica mine and some cool lookouts.  All part of the explorers tour.     https://www.nnta.ca/snow-tours   They do involve running north of the main rap loop to get too.  I’d plan to ride as many side trails between Mattawa and Deep River as you can fit in.  A lot of hidden gems worth riding along that section.  The A trail has been moved to railbed in a lot of areas.  So avoid it where you can.  The club trails west of Deep River are worth spending an afternoon on in themselves.  Big roads that are always smooth.  I’d stick to the main B trail along the south side unless you’re willing to commit to running way south towards Griffith and Mazinaw.  Top B on the south side of the park is a nice run of trail with good scenery.  Top B from Whitney west is awesome.  Definitely ride it.  But run across Redstone and Kennesis Lakes vs heading south near Haliburton.  Stay on the hydro line where the B trail heads south over Haliburton Lake.  This route saves a pile of time and is the best trails in my opinion.     If you are not running up into the North Bay Area and want to avoid Mattawa fuel can be a concern.  Alderdale General store is the solution.  It’s just north on Top D just north of the turnoff for the connector trail that runs over to the A trail.  From it you should be able to make Stonecliffe, but double check your mileage on this one.  Get fuel in Petawawa or Pembroke on the south side.  We have found fuel at Round Lake in the past, but I’d double check before relying on it.     Personally for accommodations I’d be looking at a resort east of North Bay for day 1 and would probably find a spot in Deep River or Petawawa for day 2.  Then utilize the Kennissis Redstone shortcut to get yourself back on day 3.  That way you get lots of time to explore between Mattawa and Petawawa.  Maybe consider running in the opposite direction so your last day isn’t huge, or adjust your starting point to the Dorset area.  You will need good ice conditions for this to work as there is some lake running involved.  

you only live once. do it

Well.....I'm settled on a 137 now. I have come to terms with that part. I know deep down the 600 would do the job - but there is still something in the 800+ range, it's really nice going down the lake with it. The deal on the 600 is really hard to pass up. We're talking a 9-10k swing - is the extra 258 cc's "worth" that. I think so, but I'm struggling with it. Watched a bunch of Youtube videos on the 600 last night - again, realize it would be a great sled and do the job. Will I be satisfied with it? Not sure yet.     My son is on a 550/600. He's just turning 17 soon - so I'm keeping him there for a bit still while he gains more experience, but he's already talking upgrading next year ( on his own dime   )  

Age old debate of 600 vs 800.....knowing where you ride mostly, the 6 should be great in the tighter trails, but the lakes I assume might be the the issue. It seems you ride mostly alone or with your son, family, etc.....and if they are all on the same size motor, 600 is good....running with a group that all have more CC's can be an issue.   Not really a bad thing, knowing you can buy a new sled and just need to decide between the CC's and/or track length  !