Neowin reports that the rumoured final build number 8500 has been surpassed by the latest leaked build:
Reference:A couple of weeks ago, some Internet rumors claimed that the final version number for the Windows 8 Release to Manufacturing (RTM) build would be 8500. Now another website, who has offered reliable information on this subject in the past, reports that the current Windows 8 RTM candidate build number from Microsoft has gone beyond 8500.
Winunleaked.info (free registration required) claims that the current build for Windows 8 RTM is 8506.0.winmain_win8rtm.120630-1900. Indeed, the newly updated Windows 8 Builds list shows a number of RTM candidate versions that are above 8500. If this list is indeed accurate, it shows that Microsoft is still continuing to tweak the final shipping version of Windows 8.
Microsoft is expected to finalize the RTM build of Windows 8 sometime before the end of July. That is the date that Microsoft itself said was its target when it launched the Windows 8 Release Preview version on May 31. If Microsoft sticks with its own schedule, the shipping version of Windows 8 will be available to the general public sometime this fall. The company has already announced that Windows XP, Vista and 7 owners can upgrade their PC to Windows 8 for just $39.99 from the time of its release to January 31, 2013.
Windows 8 RTM build goes beyond 8500 to 8506? - Neowin
I would suspect that Win 8 will be tweaked right up to the release date.
Complete System Specifications: By Speccy