help a nubbin with cable modem/router

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I have a netgear mr814 (v1) wifi router (http://kbserver.netgear.com/products/MR814v1.asp) and a motorola sb5120 cable modem setup in the house.

My question is that when connected directly to cable modem my download is 25Mbps and upload is 770Kbps. When connected through router (all wired btw) it drops to 6Mbps and upload is 300Kbps. In the specs for the router it list the network speeds at 1,2,5.5,11Mbps. Is it defaulting to the 5.5 in this case or something? Replacing the router definitely seems like it would work. What do you all think?

Is there a combined router/cable modem you all would recommend? I am renting the modem from comcast (for a bit until I decide and then just order it online for around 40$) otherwise and one of these from the list below.

Any picks out of these ones? Was leaning towards the linksys.

LINKSYS WRT54GL IEEE 802.3/3u, IEEE 802.11b/g Wireless-G Broadband Router
http://www.newegg.com/Product/Product.aspx?Item=N82E16833124190

BUFFALO WHR-G54S IEEE 802.3/3u, IEEE 802.11b/g 125M Wireless Cable/DSL Smart Router
http://www.newegg.com/Product/Product.aspx?Item=N82E16833162173

BUFFALO WHR-HP-G54 IEEE 802.3/3u, IEEE 802.11b/g Wireless-G MIMO Broadband Router and Access Point
http://www.newegg.com/Product/Product.aspx?Item=N82E16833162134

Thanks.