Using as a transparent proxy

Hi All.

Im looking to build a setup that I can stick in front of my HotSpots (as a separate box) that handles load balancing and proxy.

From what i can see I can use PCC to load balance (assuming it will load balance on IP and not just macs) but im unsure what hardware (routerboard) would be best for running a proxy service. Im not looking to cache tons of data, just to speed up the browsing for between 10-15 users per site where there is very slow uplinks. Will any of the RB models work with caching in memory, or do i need a USB disk as well)?

Many thanks