Lots of Windows programming using vmware fusion. The machines inside run oracle, sql, sap, etc with very large databases and I build different applications around those environments and eventually just send back the vm image(s) to companies so they do not ever need to install/set anything up. The performance part of it is needed because when running huge queries/analyzation/mining even having an extra 100/mbs will make a 4 hour analysis run in 2.
Seems weird that I use Mac, but for whatever reason, benchmarks show virtualization works much better on mac & linux as opposed to windows (even if you benchmark headless hyperv). Also, I love Mac and having just one machine to close the ecosystem is great. Not to mention I do iPhone/Ipad development for fun.
So...
I ordered the 8-core 32gb (thinking I might upgrade to 64, still haven't decided), so neither memory or cores is a problem. But having 2-3 of these running at the same time, they become very IO chatting. So it's not constant read/write since fusion queues those in memory and then dumps the data in blocks, but within an hour you will have 10-20 gigs written to/read from. Then you get into snapshots which I use often so test and then rollback changes, on average these are about 16gb written & read. Otherwise everything sits mostly ideal if I'm working on smaller stuff.
Separate drive makes more sense, but at the same time I like the idea of just having a mac with nothing connected to it (other than monitors). Also, my VM's come and go, and needed drive space goes from 400 to 800 and sometimes I have to use an external if some company has a huge 800gb image (extremely rare).
That and the price difference will be big and unnecessary. Even if say the Lacie is $1000 (I think it will be more because of pcie drives) and I buy a Mac Pro 256gb, it's more expensive then just getting the Mac Pro with 1TB
But sounds like you have experience, is it worth having a separate drive? Does it help with performance, etc? I know you don't work directly with large VM's but I can imagine it would be very similar to video editing/streaming or maybe a scratch drive.