Absolutely! In the guest role you create, you can assign a bandwidth contract.
See below
1. Configure the bandwidth contract in Configuration --> Advanced Services/Stateful Firewall --> BW Contracts (tab at top right)
2. Add that bandwidth contract to the guest role. I would make it per user and not per role. Note...the shot below is from 6.3 but the workflow is similar. The screen below will look different in older code.