Larry covered you on the hubs.
For your gearing, Id recommend you revisit it. In fact, Id recommend you dont even touch it and ride it and decide what you want.
General rule of thumb is 3 teeth ADDED to the rear, equals 1 tooth SUBTRACTED from the front.
So, in a sense, 13/43 gearing = 12/40 gearing. Most guys feel 13/40 gearing with the stock 22s, is already too high, and they want better top end power so they switch to 14/40 gearing. Especially if you do breathing mods like air filter, airbox lid removal, and aftermarket higher flowing exhaust which helps make the power you need to turn the 14/40 gears.
I dont think Id run 12/40 gearing with the stock tire size. I actually like 14/40 gearing with 20 inch banshee tires. Thats what Im running.
Heres a cool tool I made for the blaster guys that will help you in deciding what to do with your gearing. Its nice to put in different sprocket sizes, wheel sizes, to determine what youre doing to your top speed. In essence, anything that takes away top speed adds acceleration. So you pick whether youd rather have acceleration or top speed. You cant go too far on either side, cause too much top speed will make you slow through the gears, too little top speed will make you have to shift way too much, and you may end up having to shift on hills, and you dont really want to be doing that if you can help it.
Gearing Calculator
Hope this helps.