At the moment pfSense is limited to i386 and amd64 platforms - though there are some low power single board computers using these architectures.

The ARM port of FreeBSD is getting significantly more mature over time. FreeBSD 10, which is shortly to launch, has official support for Raspberry Pi (unfortunately a poor platform for a router - the Ethernet interface is a USB device). The next release of pfSense is likely to jump from being FreeBSD 8.3 based to FreeBSD 10 based.

If you're after something to connect to the BT supplied modem then I _think_ a routerboard might fit the bill ( e.g. http://routerboard.com/RB750UP)

RouterBoards look interesting, although I'm slightly wary of having to work out exactly what board offers what.

Back around 2004 when i had a block of 8 IPs from Zen i had common machines NATted to a single IP from that block, but certain machines (such as servers) NATted one-to-one to different IPs.

This was done on a Linksys WRT54GL running the Tomato firmware and was extremely simple to set up IIRC.

There are routers that ship with this functionality (i had a Draytek 2820vn that i did it on, but never again. Worst router i've ever owned) but, IMO, rather than spend lots of money on a business-class router you're better off getting one that will take a third-party opensource firmware.

Anything that will run Tomato or OpenWRT can be configured to do what you want.

As for speed, any decently specced recently released router will be able to max out even an 80Mbps PPPoE connection. A few months ago i benchmarked the TP-Link WDR4900 with OpenWRT firmware and was able to hit 340Mbps over PPPoE, although if i had a connection of that speed i'd probably build a pfSense box.

I ended up picking up a WDR4900. It is fast enough for the connection, but I do note that running a speed test from a host on the network takes around 45-48% of the router's CPU servicing interrupts, suggesting it would probably max out around 160Mbit/sec mark. That workload includes NAT as well as PPPoE.