Need more business plan details: are you growing from your current client base or are you launching a new venture?
In both cases, investing first in the backbone (scalable storage and throughput) is very wise and long term, then regardless of the computing platform you will be ok. With that in mind it’s tough to beat the utility and bulletproof and service of drobo, like this one https://www.drobo.com/storage-products/b800i/ To be sure, drobo has competitors.
You may be phrasing your question a bit off: [jeff rinland] “is the amount of power I would gain with the mac pro worth spending an extra $2000 and losing that stunning 5k display…”
Because the answer is yes, narrowly tailored to power, yet the financial question you’re asking is called Return on Capital Employed (ROCE). You will buy equipment (“employ capital”) in order to generate more earnings than the cost of the capital. So you need to know your earnings over some period of time, like a year. If those earnings are greater than the price of the equipment, good purchase. If they are not, bad purchase.