hey there!
i run a wrt-600n which is dual band and has a gigabit switch, has dd-wrt on it, and runs very well
![Smilie](images/smilies/smile.gif)
the dd-wrt firmware can be flashed from the web-ui, mini first then up to mega after... the only thing to be concerned about is you need at least 2mg flash and ideally 16meg ram but most modern routers are coming with this kind of memory as standard. You could always sell the 50meg router and put towards a new one
i haven't tried tomato, but if qos and bandwidth monitoring is as good as you say i may give it a try!
as for a router for 50meg, you need wireless N as b/g only supports about 22meg throughput as charker found out. Virgin supply what looks like a d-link 615? or could be a rangebooster? not sure, but neither of these are currently supported by dd-wrt, they are list as 'work in progress' which usually means you need to pop it open and use a serial or jtag interface to flash the firmware. Hassle.
i would recommend a linksys router as the 'n' versions are all pretty much supported by dd-wrt, and therefore tomato.
hope this helps
d