I'm still not convinced that your existing unit doesn't have 802.11n support anyway, finding anything in the god-awful menu structure on the Thomsons is non-trivial though.
Ok, I've checked that there is a mode 802.11b/g/n. The difference from my Dir-615 is that in addition to the mix mode it has 'n-only' mode. And it seems like in this mode you can have maximum speed. The N-only mode is not present in the Thompson's settings. As well, it has only one antenna.
As well, it takes 10-15 seconds just to get the first page from the thomson web console loaded. Why it's so slow?