Theoretically, if you have a device connected that's 1Gb and the other 100Mb, the 4500 should auto detect each connection and adjust for each different connection an maintain both connections at different connections. I have not looked in to this as I have my 4500 connected to a 24 pt GB switch and everything connected to it. One thing you can test, if you have a PC that's 1gb capable, and one that isn't, Connect both to the 4500 LAN ports. Look at the network settings for each PC. Look at the status section that will give you the connected speed. If the 4500 is set for auto, the 1Gb PC should read 1Gb, and the non Gb PC should read 100Mb. If for some reason the 1Gb is reading 100Mb, set the speed setting for that NIC from Auto to the static speed of 1Gb. Then check the connection speed again. I'm thinking the ports on the back of the 4500 should act like a switch and allow and maintain the highest speeds that PC NICs will support.
Let us know what you find out. I will try this out when I get home. Be interesting to know.