wireless speeds

Hi all last week i upgraded from 30mbps to 50mbps from UPC and got a new wireless cisco modem but am only getting 19 to 20mbps wireless but 40 to 50mbps directly connected to modem,my previous wireless router was a Netgear 108 mbps roeter wgt624 v4 and i was getting 10 to 12mbs download speed,i rang UPC about this but said it could be the wireless card in my laptop which is a Atheros AR8131 PCI-E Gigabit Ethernet Controller (NDIS 6.20) he said if i have a G class ill only get 20mbps or so but with a N class ill get much better speeds
Is this true and if anyone can tell me is my wireless card a G class or a N class,Im running windows 7 aceir aspire 5739g,4gb ram,500gb hardrive,intel (r) croe(tm)2 duo cpu
T660 @2.20ghz,64 bit system.

 

THANKS FOR YOUR REPLOY