You can use CAR on your FE interface to throttle this down.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios111/cc111/car.htm
The newer way to do this is using a policer "policy-map" with a rate limiter.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t8/ftpolenh.htm
This will do your BW allocation down to what rate you would like but if you are looking for a good test, the above does not account for serialization delay, PPP or HDLC framing issues, etc, you might go with Back to back serials between routers. In this way you can go much slower with your speeds using "clockrate" and better symulate end to end latency as well as BW issues.
Hope this helps,
Don