The one thing you REALLLY need to pay attention to is the massive number of warranty coverage denials. Polaris will look for ANY and EVERY reason not to fix your sled in most cases. Glue failing in a-arms, not covered, you must have hit something. Lots of horror stories to this day. I would not mod a single thing personally. I simply add oil to the fuel every ride because 70:1 stock, does not make for a long lived two stroke. I run Polaris Blue oil in my tank because dino mixes better with gasoline than synthetic, that and I have some left over from older sleds.
I am 6' 2" 225 and coming off an M7 I do not find the Polaris at all underpowered. My rides so far have been with my Doo buddies, the Cat buddies should be out later this week. I can easily hang with an e-tec Doo with a much lighter rider. My '13 Pro feels as good as the '10 800HO Cats to me. I am VERY happy with it so far, best sled I have ever ridden bar none.
I went out and did 20 miles of trail break in, took it easy, brought it back to thr truck and cooled it all the way down. After that, the snow was too good so I started riding it. Still lots of cool down breaks and keeping an eye on things. This last Sunday I had accumulated about 89 miles prior to my ride. Snow was deep, it was game on. Sled hasn't missed a beat, pulls awesome and floats through the powder like no M-cat I have ever ridden. Probably has around 120-125 miles on it now.
For now I am going to keep pre-mixing and keeping a close eye on my a-arms. Those will probably be my first "mod", a-arms that won't come apart at an inopportune time. I will be watching the compression and if it starts to drop I will most like do one of RKTechs kits, probably the pistons and head that gives 15 hp and better reliability.
Mine has a second year warranty I need to transfer still. I just do not have much faith in Poo honoring the warranty as they should. That said, before I bought the sled I had most of the above planned already. Maybe the dealer and Poo will surprise me. Maybe my preventative measures mean I will never need it.
Warm it up good, watch for the hot to cold spikes after stopping. I make sure I run it on the stand a little before leaving the lot too, mostly for the QD belt.
You may find it is perfect stock, I have. There were a dozen guys out with us Sunday, mine was the only Pro. Those boys all got lessons in what a great sled looks like pounding 3-4 feet of freshie! Wouldn't surprise me to see a bunch of them at the Poo dealer after Christmas.