I upgraded to the latest firmware (3.0.0.3.96) this morning.
Note that I do not have anything connected to the USB ports and am not using NAT loopback.
My experience with 3.0.0.3.96 so far
1. Stability:
No reboots or instability so far! (been running it for an hour or more).
2. Signal strength
With the latest firmware (3.0.0.3.96), signal strength does seem a bit lower though (will need to confirm by going back to the previous firmware and taking comparative measurements today).
E.g. on the Blu-Ray player, all the way in the opposite corner of my residence one floor down from the router, signal strength is 4 - 4 1/2 bars, as opposed to an amazing 5 bars with Beta Version 3.1.0.3.90 (note the 1 in the second section which would normally imply a newer firmware than 3.0.x.x.xx, which is strange - also the reference to 'beta' in the name is interesting).
On my laptop, using my USB wifi 802.11n adapter, it was as weak as -45 dBm (lower is better) and just now, coincidentally, -33dBm. It seems to vary, partially, just on moving my laptop about 15 inches to put it on my lap e.g. instead of on the bed beside me (without moving the adapter which is attached by a USB 'extension' cord).
3.Throughput (more relevant to performance than signal strength).
Throughput is about the same as with the previous firmware (perhaps a tad lower, but LAN Speed Test varies from run to run anyway).
4. Transmit (TX) power
- I temporarily increased the transmit power, on 2.4 GHz only (was not testing 5 GHz, from 40mW to 80mW and noticed no difference in signal strength or throughput!
(The setting is located in the Wireless section's 'Professional' tab for those who want to experiment)
I may go back to Beta Version 3.1.0.3.90 and check the signal strength and throughput of the laptop again and Blu-Ray player signal strength again (no means to test throughput on this player).
Asus official firmware:
http://www.asus.com/Networks/Wireless_Routers/RTN66U/#download
At least it is stable for me without any disconnects.
I will post after going back to the old firmware (I don't want to go back and forth more than a few times though, for obvious reasons).