I've done DD-WRT and Tomato installations. (FWIW I prefer Tomato.)
As far as boosting performance on a Linksys WRT54GL, my experience has been much the same. Not so much a boost in performance as more flexibility and stability over the OEM firmware. The supplied Cisco software works ok. But i used to have to reboot the 54GL about twice a week because it would often stall out after (or during) a larger than usual download session. Upgrading the manufacturer provided firmware only made things worse - which is what provoked me into looking into alternative firmware in the first place.
A firmware change could improve performance if
the existing firmware had a bug or some poorly implemented code in it. But it can't put something in there that isn't there already. And most of these little consumer-grade router boxes are (mostly
) debugged by now. So some of the performance improvements reported in the past are likely to be a thing of the past as well.
In general, a firmware update makes the most sense if you're looking for: stability, additional features (especially auditing and VPN niceties), or increased options when it comes to settings.
In my case, the biggest selling point is that I can install the same firmware on most of the lower end routers I need to support such that the admin interface becomes identical for all of them. That's a big improvement over looking at 20 different control panels depending on make, model, and firmware version AFAIC. But that's probably not important if you're only responsible for your own router.
Note: be very careful whenever boosting the power settings on any router's radio. These boxes are almost all passively cooled
and have power settings engineered to keep the heat they generate within safe tolerances for the device. You probably couldn't 'burn' one of these routers by selecting too high a signal setting despite anecdotal accounts of people who supposedly did succeed in "melting" or "smoking" their routers this way. But the extra power could still make them run hot enough to shorten their service life or prematurely fail.
Note 2: If you do decide to install alternate firmware, make sure to follow the instructions to the letter - and be absolutely sure to install the correct version of the firmware based on the actual version of the hardware you have. That can be a challenge with some makes (i.e. Linksys) which change manufacturing specs within a given model number. Sometimes you may even need to install a basic minimal version of the replacement firmware first
before you can install the full version you actually want to use. If so, follow the steps and don't be impatient. And above all DO NOT EVER INTERRUPT a firmware upgrade. Always wait for it to finish.
Sometimes it takes several long minutes after you think it's done
installing before the router will reboot. Don't make the mistake of thinking it timed out and doing a power cycle or hitting the reset switch on the router. That will often result in you now having an inoperable (or 'bricked') router on your hands. If that happens you'll have to choose between performing a very tedious and aggravating 'unbricking' procedure - or dropping your now dead router in the nearest trashcan.