I have several Mac Pro's, one being an up-spec'd v4 twin hex-core released 2007 that's run 10.11/12/13/14 natively but also 10.6 via a separate onboard SSD that I can select as I indicated earlier to run upon re-start. Upon shutddown it reverts upon restart back to the native OSX. Easy !
A
2007 Mac Pro is not a "v4", it's a
2,1 version and would be problematic for the later OS X versions that you cite due to having 32-Bit firmware. Perhaps you're thinking of the
2009 64-bit Mac Pro which is the
4,1 version and also accepts 128GB of RAM which you mention below.
A 2009 Mac Pro would offer better upgrade potential for later OS versions and more likely app compatibility as it has the 64-bit "
Nehalem" processor which was the first to include
SSE4.2. Current system requirements for
Llightroom Classic are: macOS Big Sur (version 11.0) or later and 64-bit support with SSE 4.2 or later. You may also be able to use
OpenCore Legacy Patcher to install later
nonnative OS versions (macOS 10.12 and later) on an unsupported
2009 Mac Pro, but not a 2007 (again because of 32-bit limitations).
The other thing is that what Apple specify as limits is not always so - the aforementioned machine was supposedly only capable of running 96 Gb RAM but happily runs 128 Gb without harming anything and uses it all. Geek Benches at 33,800. Life is a practical art, not a theory ! Consult widely and form your own opinion.
RAM capacity is unrelated to the subject of OS compatibility with specific computer models. Some models, with OS updates, may be able to access more ram than initially specified at introduction; but there are still limits as to how much of it each OS version can address.
Consulting with recognized experts who specialize in a field is helpful. A good resource for knowledgeable Mac advice would a company like OWC who can expertly advise on upgrades like
memory, drives, and more.
Another resource for upgrade information would be one which was also mentioned above, EveryMac. Again using a
2009 Mac Pro "Eight Core" as an example:
*Apple officially supports 32 GB of RAM in this model, but site sponsor OWC first discovered that it is capable of using 64 GB of RAM when booting MacOS X 10.6 "Snow Leopard" in 64-bit mode. Later, OWC bumped this unofficial maximum RAM to 96 GB running Mac OS X 10.6 or 10.7, and yet again to 128 GB...OWC clarifies in a footnote for their
128GB upgrade kit:
"OS X versions prior to 10.9 Mavericks are unable to utilize more than 96GB RAM due to an operating system limitation. 128GB can be fully utilized by a 2009-2012 Mac Pro if running OS X 10.9 Mavericks or later, or if running Bootcamp with 64-bit versions of Windows XP and later, as well as with 64-bit versions of Linux."EveryMac.com and OWC are where I would normally start to investigate the upgrade possibilities for any Mac, especially older models. They are reliable and well informed.
