Sonicwall VPN Tunnels Drop periodically

A customer has a Sonicwall NSA 4500 that has 27 site to site tunnels through a 50Mb cable connection.
Randomly they drop the site connections.  Talk to the cable company and they have seen 75Mb+ bursts which they allow apparently from time to time.  I have asked them if they can throttle it to 100Mb so, we can see if that has any positive effects.
My question is do you agree that they are trying to push too much data through a pipe that's too small and outside of running a speed test how can we determine how much bandwidth we are using?  Should we be looking at Solarwinds or some other comparable product to troubleshoot this problem?
BTW - Because of PCI compliance they are not running split tunnels so, all the traffic from the remote sites are traversing that same pipe.
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Chris HInfrastructure ManagerCommented:
What kind of Cable Modem make/model?  Some of those things punish your TCP session limit.

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