Craig, i'm not sure how "wild" the motor is that you are using but I can tell you that on my Mongoose 10.5 I run 10/49. If I ran a 12 pinion on a 45 spur i'd fry it inside of 2 minutes.
I think you can only buy the spurs in packets of 3, which include a 41, kit 45 and a 49 but i'm not 100 per cent sure on that one. The pinions I use are RW Racing and can be bought from Microtech Racing but you'll have to check the size of the shaft on your motor as I think it's a different size to the Mongoose pinions.
I can remember the Swift from at least 4 years ago so they are quite old, a friend of mine ran one for a year and then swapped to the Hong Nor.