There's nothing wrong with what Flavio suggests, just some additional factoids, you might want to be aware of.
First, you can limit egress rate either policing (drops overrate) or shaping (queues overrate). Of the two, I generally suggest shaping (which is what Flavio suggested).
Second, although Flavio suggests using a percentage based shaper, I believe your device might also support an explicit (and traditional) bps shaping too. In a usage case like yours, I think using a explicit bps value is
clearer
(QoS statements that support percentages are more useful when you want to use similar percentages on various interfaces.)
Third, I generally recommend, unless you really understand what you're doing, you use default values for optional values. In this case, if optional, do you know the be 300 ms and bc 400 ms values are better than the defaults?
Lastly, in my experience, many Cisco shapers (and policers) don't allow for L2 overhead for bandwidth usage, so you might find using 50 Mbps (however you configure it) actually overdrives 50 Mbps which does account for L2 overhead. It's easy to set a lower bandwidth rate then your nominal bandwidth, but, unfortunately, L2 overheads vary based on packet's size. Usually, I've found using a 15% reduction, for L2 overhead, works well.
