The wireless speed of your router is the LAN speed. The LAN consists of all the computers and devices hooked to your router in your house. Connections will always default to the slowest device. For example if you have a wireless N router (300Mbps) connected to a wireless G laptop (54Mbps), then the laptop can communicate with the router at 54Mbps. If you wanted to copy a file from your laptop to a desktop connected to your router via a Ethernet (100Mbps) cable connection, then you could do that at the laptop's wireless G speed of 54Mbps.
Now for the DSL speed. The Internet is the other network connected to your router via your DSL modem. The Internet is a Wide Area Network or WAN. Your DSL modem can communicate with your Internet provider at a maximum of 6Mbps. This connection bandwidth is shared by your entire LAN via your router. If one user is utilizing 4Mbps of the bandwidth that only leaves 2Mbps for the rest of the users on the LAN.
Being that your (WAN) Internet connection is 6Mbps and a wireless G router is many times faster at 54Mbps, there is no advantage in Internet speed by choosing a wireless N router. The only advantage would be in transferring files around between computers on your local LAN. Wireless N also has a larger range, meaning you can get a wireless signal at a larger distance from the router. However, remember to get either the speed or range improvements of wireless N, both devices have to be N. A wireless N router hooked to a wireless G adapter on a PS3 will have the range and speed of wireless G.
I'm not saying not to buy a wireless N router, I use one myself. Just don't expect any improvement in Internet speed. People that recommend N to improve Internet speed don't understand the concept, or they're lucky enough to live in a area and have the money to afford using ungodly fast and expensive Internet connections such as Comcast Ultimate 105Mbps.
Direct CAT5 Ethernet connections are 100Mbps, there is also a newer Gigabit Ethernet (1000Mbps) which uses special CAT6 cabling and Gigabit devices and network adapters. As with the wireless devices it will always default to the slowest standard.