In addition to everything which Don has already said, personally, I would not bother trying to run OS X on your PM8600 for several reasons. First, to get it to work on your machine is not a trivial matter, as it involves having a cpu upgrade installed, using a helper to get it installed (xpostfacto), sufficient and a lot of RAM installed, and more. Second, I've found that software runs with the least difficulties on machines of the same rough vintage. What people who've done this have said is that OS X on a converted PowerMac is very slow. Said another way, if you really want to run all the latest OS X stuff, then spent $500 and get a MacMini which'll run all the OS X (UNIX-based) programs. If you don't already have a cpu upgrade and the extra RAM, by the time you buy it you'll be on your way to the $500 Keep your 8600 to run all the great traditional MacOS programs built for OS 9.x and before. The PM8600 (and the PM9600) were two of the all time great Macs, as they are so easily upgradeable. Although the supply of old peripherals is somewhat shrunken these days, hardware can still be found out there.
By the way, there are sources on the internet for freeware, shareware, and inexpensive MacOS (9.x and below) programs - probably more than one can comfortably use. There are also a lot of cool control panels, control strips, utility programs, etc., out there which were built originally for the MacOS. Lots of formerly commercial programs have been released as freeware, too., such as WordPerfect 3.5e from Corel, and Audion 3 and Transmit 1.7 from Panic Software.
MacOS X has many benefits, chiefly its wonderful stablity and security due to its UNIX core. Now, there are a lot of new programs available for OS X, but it is a new world. Several of the neat features of the tradition MacOS are not duplicated in OS X (there are also new features in OS X, conversely.)