ASUS RT-AC68U Firmware version 3.0.0.4.374.501 ~ updated ~ 20/12/2013
Fixes:
1. Improved 2.4Ghz speed for handheld devices.
2. Fixed UI issues in OpenVPN manual client settings.
3. Changed VPN client FAQ link.
4. Fixed port forwarding issues in dual WAN, load balanced mode.
5. Fixed dual WAN UI issues.
6. Updated descriptions in VPN server.
7. Fixed issue with VPN client unable to get DNS response.
8. Fine tuned the CTF settings.
IPv6
1. IPv6 now allows LAN stateful auto configuration while DHCP-PD enabled.
2. Fixed DHCPv6 related issues.
Additions:
1. Added RSSI/PSM/SGI/STBC information in wireless log.
File Size: 28,1 MBytes, update: 2013.12.20
http://dlcdnet.asus.com/pub/ASUS/wireless/RT-AC68U/FW_RT_AC68U_3004374501.zip
With the introduction of the newer _5XX firmware, there are significant changes to the way Broadcom CTF aka hardware acceleration works, there are 2 levels now and ASUS have renamed it to NAT acceleration.
As for what are the differences between level 1 and 2, I will post more when i have the details.
Test Results as shows
Wired
Nothing new, the ASUS RT-AC68U is not even wavering a bit
2.4GHz
Very acceptable results on 2.4GHz 40MHz (channel bonding) on 600Mbps Broadcom Turbo QAM, if one is looking carefully, the ping is slightly erratic due to our ever congested 2.4GHz
environment.
5GHz
Near perfect
> 300Mbps Speedtest on 5GHz 80MHz (AC) on 1300Mbps with latency under 10ms continuously , I'm impressive

A lot of hard work is done behind the scenes. If again one is looking on my screenshots more carefully? is something up?