Go to the DD-WRT hardware compatibility list and pick one of the 802.11N units with better support and capabilities, i.e. one with a large amount of FLASH memory (16MB or 8MB or whatever) so that it can run the *full* dd-wrt and not the mini version.
Then check what people say about effective bandwidth for that model under DD-WRT to make sure it doesn't have weird limits / bugs.
For gaming systems it is often cost effective to get two DD-WRT routers, set one up in CLIENT MODE to link up over wireless to the OTHER fixed installation router which is actually wired to the broadband internet. Then (assuming your router and its switch is working over DD-WRT) you can plug random devices like game consoles or PCs into the *remote* router's wired ethernet ports and have them get online over the wired to wireless to wired setup you'll have. It is especially good to do this when more than one console / PC in the same area can link in through the wired ports on the client mode router.
Doing that will save you wireless congestion and improve your overall transfer rate as opposed to having that many more *individual* wireless NICs fighting for bandwidth. And of course it is cheaper than some of the dedicated "gaming to wireless" link devices.
Put a reasonable omnidirectional antenna on the main router that feeds the house so the signal level will be better for all and thus better bandwidth. In a large place, and especially if you do use a client mode auxiliary router that handles multiple devices if can be handy to add an omni antenna to that too.. $8 gets you a decent omni antenna from various places like Fry's or online.
Now realize that even if your cable service is 8Mbit/s, that is a pretty LOW bandwidth compared to 802.11N's capabilities which can often feed 40Mbit/s to a given peer PC (though of course that divides based on the number of simultaneously active peers). But even 40Mbit/s (a very conservative number for 802.11N with any kind of reasonable signal strength and not huge interference) divided 5 ways is still 8Mbit/s for each peer, so basically full possible *internet* bandwidth. In reality you'd do better than that due to various idle times and some devices being off or very close or whatever.
If you really want to maximize *broadband* cable bandwidth and performance you'll need a QOS system in place. Some of the "gaming" routers like the DGL-4300 or better have QOS capabilities, and I'm sure there are better models than that nowdays. It is irrelevant what the router does intrinsically if you load DD-WRT on it though.
Check to see if DD-WRT has any traffic shaping / QOS functions in it, I forget what it has. I usually use a dedicated LINUX PC based QOS router and file server and mail server and web proxy etc.
Anyway the idea is to artificially cap the bandwidth of the outgoing service from the router at a little less than the actual real normally achieved peak bandwidth of your cable service. That way the outgoing data bottleneck is always at the local router and not in the modem. Then you have a traffic queue/buffer of data waiting to go out to the internet in the router when things are busy at a higher bandwidth than your broadband can support. Prioritize the SMALL size packets like ACK packets and connection establishment packets so they jump the line and go out first. Then allow "user interactive" traffic like SSH, telnet, game console packets, small HTTP/WWW packets out next. Then lastly allow out big packets like max. MTU size P2P uploads, FTP uploads, and so on.
Overall your effective smoothness and usability of the bandwidth will be MUCH improved over doing nothing; this is true even if you used the setup BY YOURSELF, much moreso with multiple users.
You probably get better QOS control if you used a LINUX PC router or something but I suppose DD-WRT if it has it or some other QOS routers fairly default setups are probably better than nothing if you configure them appropriately.
If you want to further imrpove things, you can use a PC with LINUX to set up a SQUID proxy for the WWW and a cacheing DNS recursive server so that frequently requested pages like google or CNN or BBC or whatever stand a better chance at being cached locally so any page reloads or page navigations within the same site that use the same stylesheets / icons / images / banners / whatever will tend to instantly be served at least a good percentage of the time from the local cache. You can turn up the CACHE setting on your WWW BROWSERs to achieve a similar effect for WWW traffic.
If you're going to run a local file-server PC or NAS or something then you'll potentially want higher bandwidth than internet bandwidth to talk between machines on your network for local access P2P or local backups or whatever. 802.11N may still do a decent job of serving you even in this case, though obviously it won't be the same as having a wired gigabit LAN.
If you really saturate your cable pipe, pay for two independent DSL / cable services and set up a router or two to load balance between them. A PC based router could do it easily, though if you want to do it with a wireless router you're probably going to have to set up two parallel 802.11N routers one on each internet connection with different SSIDs and IP assignments and just have some people connect to one and some connect to the other.
There are other things you can do at the networking layer but these are the most basic / effective.
