GiGE performance question(s)

Anyone out there have any Cisco GigE operational experience? I've got a customer who's evaluating GigE to 100 switched Ethernet, and they want a homogeneous vendor network (I don't know why, I just help them write the trade study...) So far, there's a huge question about Cisco GigE to 100 switched performance and I was wondering if anyone's willing to cough up numbers. Although, if there are numbers for other non-Cisco vendors, they'd be helpful ammo as well. -scooter