I've been taken by the USDigital H-5 series of shaft encoders.
http://www.usdigital.com/products/en...otary/shaft/H5
I started using them several years ago, when I couldn't get the Greyhill ones fast enough (EVERYONE was out of stock at the time, Mouser, Digikey, Newark).
Turns out, I like them better than the Greyhill 63R because....
1) 10K RPM versus 5K. (our shooter motors ran over 6K RPM)
2) Locking, captured signal cable, doesn't fall out, nor likely to break off the header pins.
3) Discount for FRC Teams.