C5, C7 V2 and C8 etc. improved the compatibility with DLNA devices and enhanced the overall performance. That's all I know.

Follow the following guide to check your settings. http://www.tp-link.com/en/article/?faqid=771

With the first W8960N, do you have the same problem? You'd better test WLAN to WLAN speed using some other wireless clients to make a comparison.

Try to change settings as below. Mode: 11bg mixed Transmit Power: Middle Disable UPnP If they won't help, submit a ticket to TP-LINK support team. http://ticket.tp-link.com/index.php?/Tickets/Submit

WR1042ND has no feature to disable NAT. WR1043ND V2 has the feature. Why you don't use WR1042ND as an access point instead of a wireless router?

Here it is. http://ticket.tp-link.com/index.php?/Tickets/Submit