It looks like ASUS still improving firmwares for old routers. Last original firmware L2TP speed tested.
Original FW_RT_N16_3004354 (2013-03-22)
http://ru.asus.com/Networks/Wireless_Routers/RTN16
Alternative 1.9.2.7-rtn-r4923 (2013-03-16)
http://code.google.com/p/wl500g/
upload speed not limited by router performance, but rather by Kyivstar (ISP) at prime time.