If you want performance than you have to go for the 100Mbit Switch.

It has no point to use 100Mbit for Internet traffic cause your connection to your ISP probably isn't that fast. But the 10 NIC's cost almost the same as the 10/100 NIC's so...

My suggestion:

cheap Linux box with two cards:
10 Mbit NIC for Internet WAN (connects with xDSL / Cable modem, WAN backbone)
10/100 Mbit NIC for LAN (connects to 100Mbit Switch)
and with 'BBIagent Linux NET4' you don't need a HDD.