Well, I have seen speed degradation on wireless as opposed to wired LAN in every case I have tested.
802.11b is 11 Mbps and is definitely going to slow your connection down. When I used this my 4000 Kbps connection (at the time) slowed to about 2000-3000 Kbps when I was not too far from the router. The farther away you are the worse the problem.
802.11g is 54 Mbps and will increase your range quite a bit. You should see allot less degradation of speed because of the higher bandwidth and the increased range. You will also have much better range through walls and obstacles.
Now on to the newest shit out there. Pre-N - Now, Pre-N has not come out yet but Pre-N stuff has. Belkin offers a Pre-N router for about 159.99 and a laptop card for 109.99 see this at Belkins Site (direct link to router). Below are some of the listed advantages... stuff in green are advantages over old technology.