I have moved up with each new release(after a waiting period to see if its not a disaster
). If you are on PT9, moving to PT 10 would be pretty much painless as all plugins should be fine(and PT10 added Clip Gain, which is a major plus). The other reason to move to 10(for me) is that the file format changed, meaning PT10 shares the same file format as 11, 12 and up. So if you collaborate with others that run 10/11/12/etc, sessions will move back and forth with relative ease(going from the newer versions to PT9 requires a Save Session Copy>select the 7>9 format so the session will open on your PT9 rig(if you're not sharing sessions with other users, then this is probably a non-issue)
Now, building a new machine probably means new OS, so consider; PT11 and up is a full 64 bit program, so a new machine with a quad or 6-core cpu and 16GB(minimum) RAM will give you a serious performance boost. PT9/10 are 32 bit programs and can't use more than maybe 3.4GB of RAM. Seems a shame to build a new powerhouse computer but not be able to take advantage of all that power
Windows 10 takes some getting used to, but to me, it seems more streamlined. Plus, using a fast SSD for the C: drive is a no-brainer. Samsung 840 or 850, EVO or PRO are my choice(500GB), but many new motherboards can take NVM(probably incorrect nomenclature) drives that fit a slot and are stupidly fast.
Downside of moving to PT11 and newer is that you will be installing EVERYTHING from scratch. Upside is, you really should do that anyway on a new build(putting an old system drive in a new computer is just not a great idea). You will need to update every plugin you own as 11 and up ONLY use AAX64 plugins(RTAS is dead in a 64 bit world). Also, there are a handful of plugins that either never made it to AAX64, or changed enough that opening old sessions just might force you to swap out some plugins(example; your Digirack delay plugins for short, medium, long, extra long; have all been replaced with a single delay plugin). The new plugin can DO everything the olds ones covered, but you will need to recreate your settings from scratch. There are several other major features that make moving up a worthwhile change. Its up to you whether you want to deal with the growing pains
