I think the whole house would benefit from a better wireless router than the HH3. I was going for the Draytek 2750 as its a combined vdsl modem router but, it doesnt do simultaneous dual band.
Having been a draytek fan for years, and currently running a 2820 connected to my openreach modem, I've just ordered an ASUS RT-N66U as reviewed by MrSaffron on this site. Its a lot cheaper than any draytek kit and I prefer connecting to the openreach modem rather than trying to replace.
For WiFi I would strongly recommend using inSSIDer (on Windows) or WiFi Scanner (Mac) to look at what is around you first, and see where the problem points are.
At 2.4 GHz using the 40mhz wide mode on N is generally very unsociable as you take over 2 channels and in a crowded area you'll find you get worse performance than a single channel at 20mhz.
At 5 GHz using 40mhz wide mode is obvious, but the higher frequency doesn't always get through the walls very well.
James BT Infinity 2 19/09/2012 - Speeds ~46 / ~8.5 Mbps - Sync 48.9 / 10 Mbps @ 470m
Huawei modem -> Draytek 2820 -> Airport Extreme -> Switch -> Windows/Mac/Linux/NAS/Phone/TV
13 years of broadband - 1999 ntl:(512k/1M)/BTbusiness(2M)/Metronet(2M)/Bulldog(8M/16M)/BE(19M/16M)/BT FTTC(46M)