Wireless vs WAN disproportion

I have 100/50 Mb internet connection. Everything is ok using metallic connection (90/45 Mb max). But on wireless max speed I can reach is about 30?/45 Mb.
Wireless seems to be ok because LAN transfer (between NAS and notebook) reaches 10000 kB/sec.
Trying to reset the router and use just the default configuration - no change.
my router is 751G-2HnD (fw. 3.17)

Any advice?
Thanks
PK.

What device is connected to the wireless (laptop?) and how did you test?

Yes, notebook (HP EliteBook with Intel Centrino Ultimate- N6300).

tested on number of internet speedmeters. I checked download speed of some higly seeded torrents too.

Of course I verified it with my internent provider too. As I said when connected directly (without router) or using cable to connect to the router, the speed is as requested.
Using wi-fi, the upload is still ok but the download speed gets down to 1/3.