looks like theyre pretty long... from a quick look looks like you'd need at least a 108, 106 only has a 25nm output torque below 1500rpm, even a small 6374 motor would come close to exceeding this on about 2kw or so... unfortunatly if im reading it right the 108 is 1bout 18cm long... and to get a resonable safety margin for the big 80100 type motors you're looking at the 110 - 24cm long! kinda hard to work with on a bike. the a nugart pl80 would be better, about 10cm long, 100nm output, 2.5kg, 6000rpm input. if you can wait for a deal they pop up on ebay at around the $3-400 mark occasionally. ple8090 is basically the same thing if you happen across one too. you might get away with a ple60 on a low power setup (there about 40nm output from memory).
data sheet if you needhttp://www.neugartusa.com/Produkte/E-cat-08.pdf
email them and ask for USPS shipping instead of ups - mine was $40 rather than $185 for my ple80 (to australia) took about 2 weeks.