I believe 100mm or so is appropriate for dirt jumping with the bros.
100mm for general trail riding duties on a Bfe would be a bag o ringpiece, hence recommendations for longer travel.
100mm is ok for trail riding, but I guess it depends what trails you ride! I just mince about on fairly mellow trails like the guy in the video below (he’s using about 100mm of travel)
I imagine most people on here probably ride much faster and on gnarlier trails so they need all the extra travel.
[video]http://www.youtube.com/watch?v=u2gs214G7gw[/video]
I got my Pikes off here, I think they cost me £185 and they are 454 coils. If you get the cheaper 426/409’s then you’ll probably pay £150.