Cable to UTM bridge - Bottleneck or not?

Hey Spiceworkers,

Has anyone had experience in bridging a cheap ISP provided cable modem to a business class UTM router?

I am confused about it. I thought that when the cable modem is in bridge mode, the connections pass through the cable modem to the UTM router. But the cable modem will still create a bottle neck at the end of the line? Meaning that 50 users on the UTM would have problems with the VDSL connection?

Usually i would have the cable modem in bridge mode, then have all the NATING and WEB filtering etc on the UTM.

Please correct me if i am wrong :)

Regards

Phil