Thanks for the help guys.
I should have clarified my qn. I've been through the wiki and trolled the linksys forums so I know where the latest fw depositories are. Basically, I was looking for assistance on choosing one of the numerous versions of fw available and the information on them and their naming conventions do not make the choice simple. I knew I had to keep it under 4Mb RAM.
I settled on 'Tomato Firmware v1.28.7633 .2-Toastman-IPT-ND ND USB Lite' and so far all seems well, even though is got stuck rebooting after I customised the settings and has crashed once. But, since then it is running smoothly.
Well done to Toastman for the preset QoS rules and settings. It really has made things easier.
So far I have found Tomato to be more responsive and stable than the custom Asus fw with more effective QoS settings, but I was confused by the numerous options as there is no built-in help file associated with Tomato as is in DD-Wrt (which ironically I found easier to figure out even with its greater customisations).
Is there any value to installing tomato on more recent routers as I'm assuming that the hw and stock fw has improved a lot over the last couple of years?