Hardware site AnandTech has posted an extensive review of the fifth generation AirPort Extreme base station and the fourth generation Time Capsule, and while you may not want to read the entire 9-page review, it's worth popping to the end, where author Brian Klug explains how an internal hardware change (from Marvell to Broadcom) gives these new models improved throughput and range. follow link
Improve Apple Services with AirPort Base Stations
You can make iChat file transfers, iDisk, and Back to My Mac work better by turning on a setting with Apple AirPort base stations released starting in 2003. Launch AirPort Utility, select your base station, click Manual Setup, choose the Internet view, and click the NAT tab. Check the Enable NAT Port Mapping Protocol (NAT-PMP) box, and click Update. NAT-PMP lets your Mac OS X computer give Apple information to connect back into a network that's otherwise unreachable from the rest of the Internet. This speeds updates and makes connections work better for services run by Apple.
New AirPort Extreme and Time Capsule Feature Improved Throughput
Check out the Take Control ebooks that expand on the topic in this article: