If your network has hubs, that could definitely be a problem (force half duplex, generally slow things down). Also, I must point out that forcing full duplex instead of auto can break certain computers' networking. There's a whitepaper from Cisco around somewhere about it. I spent many moons trying to figure out the problem (not having access to the switches...). Also, what kind of backbone is there? If it's just a 100 Mbit backbone, you're toast. Also, if your servers are all on 100 Mbit, you're toast. Fun stuff...
