I don't play many twich / shooter games anymore but have played quite extensively over wireless for the past year.  Below are some of my thoughts and info.
THOUGHTS:
- The difference in speed has been negligible, that is if and until your wireless connection is interfered with or dropped.
- Use a wireless NIC that comes with it's own connection management software (i.e. allows you to NOT use Windows' Wireless Zero Configuration.)
- Get rid of any cordless 2.4Ghz phones in your house/apartment.  Mine conflicted with my wireless network, on every broadcast channel, causing my connection to drop for the duration of the call.
- Consider getting hardware that supports 802.11A.  It's more expensive but is supposed to be faster, cover a wider area, and provide more bandwidth.
- Consider using the same manufacturer equipment for your NIC's and router to take advantage of any "Speedboost/Turbo" features that they offer, but that are usually not compatible across OEM's.
- Keep your network away from your microwave.
- Try the various security options WAP vs. WEP-PSK to determine for yourself whether or not the overhead is noticeable.
- Use of some form of security is a must.
INFO:
- Aside from having to replace it, under warranty, within a year of buying it I've been very pleased with my Linksys router.
- Windows XP Pro SP1
- Play on a notebook with a Linksys PC card.
- Have played games including Tribes2, Tribes Vengence, City of Heroes, Asherons Call, Splinter Cell PT, Unreal Tournament, etc.  with little to zero noticeable lag.
- Have played wireless using both DSL and cable connections.