Hmm interesting, if you don't mind me asking what sort of cost are you looking at for TGM? And what sort of hardware are you using to try and guarantee 10Gbps worth of Firewall throughput?
As a point of comparison, I don't have a Cisco price list to hand but for a Checkpoint box capable of shipping 10Gbps of firewall throughput your looking at around $56-60k.
Cisco wise you'd be looking at a ASA5585-X with a SSP20 or SSP40 to get to 10Gbps Firewall throughput, I can't see them been any cheaper than the CP box if I'm honest.