The bandwidth does not affect the speed data is transferred over a interface and that is all interfaces not just tunnels.

It is basically just a number and you can set it to anything you want. The true transfer rates are set by the physical clocks on a interface.

You will always send/receive data at the interface rate even if you leave the bandwidth set to 9k

This parameter is used

1. By some routing protocols to select path. This needs to be set correctly for the router to be able to select the proper "best" path. Be careful running routing protocols over a tunnel you must avoid learning the tunnel end points over the tunnel.

2. QoS For a tunnel it is of limited use to run QoS but in some cases where you want to limit the traffic it can be effect to apply QoS to a tunnel.

3. Many monitor tools read this value via SNMP. Mostly this stops calls in the middle of the night from your NOC guys worried because their tool said the tunnels was utilized 3000%

Using tunnels to run routing over MPLS is one of the more common uses lately. You really won't have a issue leaving it at 9k as long as you leave all your tunnels at 9k. Just be consitant but it is best practice to set it to the physical interface speed.

In your case this is the simple way to run routing over a MPLS network. You can do what you want without involving your provider. If you have many sites with any to any conectivity it gets complex to maintain all the tunnels and you are better off running BGP directly with your provider. Once the BGP is setup you have a lot control over routing within the cloud but still not to the level tunnels allow. All depends on how large a MPLS network you have.