Following our recent report on the “Mac Pro build” of OS X Leopard, 9C16 and recent seeds of 10.5.2, Apple has posted a new seed for third party developers to evaluate, 9C23. The already extremely lengthy changelist and fast-growing update package is now over well into the hundreds of megabytes and could eventually exceed 400MB(!), making it the single largest point update to OS X ever.

Depending on whether one is updating a PowerPC or Intel Mac, packages could vary from 250 to upwards of 400MB in size, and some on the grapevine believe its final weigh-in could be very close to five hundred megabytes.

Either way, it will be a huge download and there has been a lot of debate at Infinite Loop, according to reliable sources, as to whether the update should be split into multiple packages (the core system update, and individual updates to applications or components), hold back some changes for Security Updates that will follow shortly after the point upgrade…..or a more unusual solution, such as offering the update with a nominal pricetag of a few dollars on a CD-ROM disk for purchase at the Apple Store, to ease the burden on modem users or others for whom such a massive download is impractical.

For the rest of us, in the broadband age, a 500MB download isn’t such a big deal, but it will still be a huge strain on Cupertino’s bandwidth at a time when things like HD movie rentals and other new offerings are already rapidly expanding Infinite Loop’s bandwidth usage.

To prepare for the update, which was originally slated to have already been released but due to a huge changelog and the need for extra upstream bandwidth to be allocated for the huge surge that the Software Update release will bring, Apple’s network engineers have been frantically working overtime and on weekends to install new fiber, routers, servers and infrastructure to be ready for this.

One 500MB download might not be enough to bring Apple’s servers to a crawl on their own, or even coupled with the new HD movie downloads and ever-growing iTunes Store…..but Apple is also about to begin offering iPhone applications for sale and has a “major new .Mac related offering” to announce in March — about which we will soon be rumor-mongering, so stay tuned on that! — so adapting to all of these needs at once has proven quite a challenge for the usually unflappable network techs in Cupertino.

According to reliable sources, the final release of 10.5.2 will most likely come around build 9C40 and should arrive well before the end of February — quite possibly in as little as two weeks, if Tron’s latest “postcards from Silicon Valley” are accurate — so stay tuned for all the latest OS X update coverage and all the dirt that’s fit to print right here on Mac OS Rumors!