I don't like iso flex in doo 600's. The poo's the crank bearings are lubed via oil pump. 

Poo 650 may not get the same MPG as Doo 900 na, but it is closer than you think. As signfan says, the current Matryx Poo has 43 L tank to the current MXZ having 36 L. Be it 129 or 137, Matryx Polaris 650s are remarkable trail sleds. To be fair, I have not ridden the 600R MXZ. Mid City Motorsports in Sudbury is still advertising new 2024 Polaris models for $13599 (129) and $1499(137 with 7s display). 

I own both a 900 ace and 650. On trail 650 will be really close. Next week I run them side by side. Wife going to drive Polaris and I drive 900 ace.  Imagine they be within a 1litre or 2 of each other for similar distance driven.  650 is very good on oil too. 

Polaris has a 43.5 litre tank.  XS chassis 900 ace is 40 litres and a g4 or newer doo is a 36 litre tank (unless it’s an expedition or scandic which are 42).  So it could have similar range.  Curious what the math works out to for actual fuel economy.  They will all do 300 kms with one of those linq cans on the back.  

I will tell you from personal experience on our 2024 Polaris 650 XCR that we took to Longlac a couple of years ago, It is 150 miles/240 kms that the 850 sled made to 130 miles when all the 850's and Doo 900 turbo ran out and we kept riding it to see how much was left in the tank, got to Longlac and it still had about 13 litres of gas left in the tank so would have easily gone about 200 miles/320 kms before it ran out, So yes that puts it in right in the range of the 900 Ace non turbo for Range. Bear in mind we all kept our speeds down in trying to be mindful of getting there. We are heading that way next week and will be seeing how the new 2026 650 does vs the 2024