Some may find this to be an interesting weight comparo. Had to dig it out of my archives over on Dootalk to remember the numbers, but I found 'em:
When I purchased my 2010 Renegade 1200, I still had my 2008 Switchback 700 Dragon sitting in the garage. Both machines, sitting side-by-side, both showing about 3/8 tank of fuel, both full of oil/coolant and ready to ride. I grabbed 3 old bathroom scales I keep out in my shop and set them under 3 locations and came up with the following:
10 Ski-doo 1200 Renegade Adrenaline: RF spindle 176lbs, LF spindle 165lbs, Rear 222 lbs = 563 lbs total
08 Polaris Switchback 700 Dragon: RF spindle 177lbs, LF spindle 165 lbs, Rear 239 lbs = 581 lbs total
I was so shocked when I saw the numbers I shuffled the scales around and did it twice. Same results give or take 2 lbs.
Confirmed: My brand new 4 stroke, electric start, 1200 actually weighed LESS than my 2 year old 2 stroke, pull-start, batteryless 700 Polaris. Both same track lengths, both in ready-to-ride condition with partial fuel fill.
Did they have exactly the same amount of fuel in each sled? Doubtful. Was this entirely scientific? No. But it still said something to me...anyone on an older chassis 2 stroke, considering switching to a newer chassis 4 stroke? You might actually LOSE weight in the transition...or the difference will be too small to ever notice a difference.
Now...if I compared an 800 Ski-Doo to a 1200 Ski-Doo, obviously the 2 stroke is lighter. But Ezra's comment about "overcoming an extra 175 over the skis" is a gross exaggeration by a factor of at least 5. Doo as an example from their spec sheets:
1200 Gade: 532
900 Ace Gade: 503
ETEC 600 Gade: 481
The weight penalty of a 4 stroke can be as small as 24 lbs...or as much as 51 lbs...depending on your engine choice. It is directly over the skis, and my Doo is more nose-heavy than my Polaris was. Wider aftermarket ski's help compensate for it. But the penalty is certainly not anywhere near 175 lbs...
All that said, if I go mountain riding, I'm renting a 2 stroke. The difference off-trail in TRUE deep powder, and when climbing, is very real.