Who is this Mac Pro for?
1. You need more than 2 PCIe cards (3+ T3 enclosures is a bit much IMO)
2. You need > 4TB of very fast storage (Might as well vs Apple's $2K 8TB)
3. You need an x8 Audio Video card of some sort?
4. You need > 10GbE networking (Thunderbolt can't really fully handle 25GbE. 100GbE is actually surprisingly somewhat affordable)
I'm team want #2 and #4, but need none of these.