I used the WRT54G extensively in the examples in my 802.11g NeedToKnow, and will just repeat some of that information here for your convenience. Although as I was writing this review, new firmware was released for the WAP54G that incorporated changes mandated by version 6.1 of the 802.11g draft standard, Linksys had not yet released a similar version for the WRT54G. So the results you see here reflect the performance provided by 1.01.4 router firmware and original WPC54G client drivers.
I also won't be spending any time discussing the ins and outs of draft-802.11g throughput testing. Again, if you want the background, read the NeedToKnow. I'll only say that to get an accurate picture of what draft-802.11g products will deliver in the throughput department, you need to test under three scenarios:
Without any 802.11b clients active
With an 802.11b client associated to the same draft-802.11g access point or router, but idle
Scenario 1 - No 11b active
Figure 8 shows the first scenario and with WEP disabled and with the router set to Mixed wireless mode.
Figure 8: Four Condition Throughput test
The "warmup" effect that I found in my WAP54G testing appeared to be solved by the newer firmware and the 21Mbps average throughput under Condition 1 is the best of the draft-11g products that I've tested so far. I didn't try to find the limit of the range of my test pair, since I was seeing signs of being close to the range limit similar to those that I see when testing 802.11b product. It's worth noting, though, that my worst-case Condition 4 throughput of about 4.8Mbps is about equal to the best throughput that typical 802.11b equipment provides.
Also in Linksys' favor is that enabling WEP doesn't appreciably affect throughput, as shown in Figure 9.
Figure 9: Test Condition 1 - No WEP vs. 128 bit WEP
The summary for Scenario 1 then, is that the WRT54G does pretty well with no 11b competition around and with a Linksys client card.