As far as the Mobil 1 synthetic gear oil, I can only get it in 75W-90. Mobil may offer different weights in their regular gear oil, but I've never seen any other weight than 75W-90 in the synthetic. The difference in the Mobil 1 gear oil versus the Polaris tranny oil is that the Polaris oil is a little thinner. However, Mobil 1 synthetic gear oil is much thinner than petroleum 75W-90, and is only marginally heavier than Polaris'. And yes, I use that same gear oil in the front gear box as well. As far as the Mobil 1 synthetic ATF, that's what I use in the front hubs. I change it probably more often than necessary(about once a month), but have never had any problems with the hubs sticking, ever. A quart of that ATF costs about $5, but will go a long way since each hub holds only a couple ounces. Most of us probably know, but I'll give my procedure for changing the hub fluid:
1) Remove the wheel first. Upon draining the hub, fluid will get all over the wheel if it is left on the bike. This makes a pretty good mess and can be avoided easily by removing the wheel. This also gives you the opportunity to easily check the condition of the brake pads.
2) Drain the hub.
3) Wipe clean the magnet in the drain plug. That black stuff collected on it is wear metal from the hub. Unless there is actually larger pieces than fine metal powder(wet with oil) on the magnet, the hub should be in good condition. If there are larger pieces of metal stuck to the magnet, I would tear the hub down and inspect it for damage or have a mechanic look at it. If the fluid in the hub is ever milky, that means water has gotten past one of the seals and one or all of the seals needs to be replaced.
4) Turn the plug hole in the upright position and refill. To assure the correct oil level, you can check by turning the hole to the 4 o'clock position (recommended by Polaris, however, I use the 3 o'clock position and have had no problems). At this position, fluid should barely seep out the hole. If no fluid seeps out, turn the hole back to the top position and continue adding until fluid only seeps out at the 3 or 4 o'clock position. If fluid runs freely out at the 3 or 4 o'clock position, you should leave the hub turned to that position until the hub has drained down to the proper level.
5) Replace the plug, being careful not to overtighten.
6) Wipe clean the outside of the hub, as there will be a good film of fluid on it.
7) Replace the wheel and tighten the lug nuts.

 

The price of Polaris' 0W-40 at my dealership is about $5.50 per quart versus about $4.20 per quart for the Mobil 1. Not a significant savings, but the availability of the Mobil 1 is a big plus for me. I guess if I looked at the extra time and gas for going further to the dealership, I'm probably saving more than $1.30. However, if I buy the oil at Wally World, I always pick up other stuff I don't really need, so I would be just as well off just buying from the dealer. Regardless, either oil is excellent, so convenience is probably the biggest factor. Note this: Read the warranty requirements listed in the back of your owners manual. While under warranty, it is best to use Polaris' lubricants to eliminate voiding the warranty if something should go wrong. Polaris will not warrant repair if you don't use their recommended lubricants. In the maintenance section of the manual, they specify Polaris Premium Synthetic 0W-40 motor oil and Polaris Premium Synthetic Chaincase oil for the rear tranny. However, they don't specify their oils for use in the front gear box. I did use Polaris' oil until my 6-month warranty ran out, but now use Mobil 1. I just put this in here for all to see and make their own choice on lubricants.