Networked Storage - Large USB 2.0 or SSD in caddy

I have a Belkin N+ gigabit router with a built in USB Port. I originally used this to plug in an Enclosed Raptor Drive for my media along with another standard 7200rpm for simple backups. However those drives have now been put into a DIY NAS and made in RAID 10 arrays for some sort of redundancy. Which leaves me with a free USB port on the router.

I was thinking of purchasing a USB key to store on my CD images and plugging into this port. This way I can access CD images remotely without putting extra burden on the existing hard drives, especially when most of those ISO files will be mounted on multiple hosts as a time. Which now leaves me with two choices

64GB USB 2.0 Key or an SSD in an enclosure? Apart from the initial download of the ISO files I would be most likely be using this drive for multiple reads at a time so high read speed is important.

Thanks in advance!!