Best way would be SQM, I’m planning on using an Openwrt Router in-between my Hardware and original router to use it.
@arrogantrabbit did a post about SQM and its benefits (it almost does everything by itself):
Capping is more likely a quick and dirty way.
I know, that StorJ wants to offer full speed to the customer, but in the end its all private people offering their bandwidth, and if it surpasses the available bandwidth, now wonder some would rather limit Storj, than their own speed.