Please do! Let us know at what mW setting it starts to melt. "Got 5 bars in every room, but then it started smoking". "Now where did I put that old Amped router anyhow"?
I would not suggest putting it too high which is why I mentioned 100mW.
In fact, given existing firmware's wifi performance, I had long been suspecting the so-called "40mW" current setting might just be a typo (and in fact really be something like 100mW which is what some Linksys units have as a default), maybe that is what they are fixing since I doubt they want a ton of units returned due to overheating...
Also:
1) Unbalanced conditions can arise at certain levels:
You can only go so high before it gets too unbalanced (although it would still increase one side of it)/
It would increase transmit range but not receive range since the client still can't "talk" any louder or be heard better (luckily the RT-N66U has good antennae which help it to pick up weak client signals better than some other routers, but there is still a limit to what amount is useful).
2) Going too high (experimentation could help tell what level that is) eventually increases noise (distortion) too much and will actually have an adverse effect.
The two points above are
not from the following article I found as I was about to post, but it is interesting anyway:
Article about TX power
http://tomatousb.org/tut:increasing-wrt54g-transmit-power
I also did just notice as I am about to post that 250mW is REPORTEDLY being used without problem with some routers. However, who knows which model router they are using.
I would not try running a 1995 Yugo or Hyundai engine at the same levels as a Ferrari...
I would suspect (experts correct me if I am wrong) that given that different router brand / models are designed differently (different boards, capacitors, heat sink, venting, CPU, firmware etc.), a TX power that might be safe for one router might be unsafe for another design.
http://tomatousb.org/tut:increasing-wrt54g-transmit-power
Maybe Asus (engineers) can explain what the next firmware update will really do for TX power on an absolute (and properly calibrated) level and what the "40mW" really equates to (I doubt it is really going to go from 40mW to 500mW but I could be wrong...).
I will give the support line a call or send them an e-mail for clarification...
My performance is fine as it is, which is why I suggested I personally may not even touch it except for temporary experimentation, still not going any higher than a safe limit (even short term I would personally be leery out of caution on my own part - others says some levels are okay for the short run but would eventually burn the unit out - I don't like taking chances especially when it is working great as-is).
(I might venture to experiment temporarily with 100mW in the updated firmware [which may even actually be the current "40 mW" displayed value (could be a bug and incorrect], given current performance rivaled my Amped R10000 which had the best signal of any router I tried, including recent models like the E4200 v1 and Zyxel NBG5715).
Long story short, I would be careful setting TX power too high for fear of affecting stability in the short run and wear and tear concerns (burnout) in the long run.
I have edited my other post to add some clarification thoughts that were running through my head but I fell asleep (passed out is a better term) before 9 PM which is extremely unusual (still way behind after at least 15 years of never sleeping nearly enough lol).
I woke up at 9:15 PM or 9:30 PM and, until I saw the time, thought it was 4 or 5 AM!!!