I have the same question, but not in regard to memory use, as to what it seems the original poster was alluding; I am wondering more in general, and this is for an ol' WRT54GS, on which I can use either the 2.4 or 2.6 MIPS1 firmware. I ran the 2.4 for a while, and then switched to 2.6 for build 54, while testing QoS and other things. I've noticed that I seem to get random internet dropouts, usually for a 10-30sec. I tried disabling QoS, and all the custom scripts, etc; but made no difference. The dropout seems to affect DNS; but not audio/video streaming as much, although I have had streaming stop too (but didn't verify that other websites were down, as the wife would be waiting for netflix to come back…). Chat clients will disconnect. One time, the router spontaneously rebooted while I was online (it was the only time, as I now check the uptime periodically because of that).
Anyway, I spent quite some time, around the 52-53 releases, trying to find some comparisons/pros/cons of 2.4 vs 2.6 on the WRT's, and found little (which is why I decided to just try it). That is, I found lots of others asking the same question, but not much for answers. In fact, most of the tomato variants don't recommend/provide 2.6 for WRT's at all; I recall only here and victek provide for it (going from memory here). Though, the driver used varies too amongst the variants, so that might be a bigger factor than the kernel…anyone have thoughts on all this, or similar experience/testing? Anyway, I plan to go back to 2.4 for the next release (which appears to be soon, from what teddy said in another post), use mostly base settings, and see if the dropouts do actually go away. If so, I can start changing things to how I'm setup currently, and see if issues start to arise.