Hmmmm, now with this #KPTI issue (what a cock up) the performance degrade potential (some are saying as large as 20%) is something one has to contemplate. If macOS (Mach) is indeed affected this will cause a massive recall event for Apple. This is a real bummer and sincerely hope Apple announces something soon about a fix being needed or not and if a fix is required what the performance hit is likely to be, and not just for the iMac Pro but for all the other Intel-based Mac as well.
Getting back to the OP subject...
I ordered my CTO iMac Pro early AM on Dec 15 (10core/128GB RAM)/1TB SSD/Vega 64/KB/Mouse) and it's not even inline for manufacturing yet. That is, my iMac Pro has not even stated to be built. I still have the opportunity to cancel my order at this time and save myself the issue of not being able to return a CTO machine. I believe CTO Macs cannot be return (Please correct me if this is incorrect). I will give it another day to see how this #KPTI issue plays out and if there's no additional info I will be cancelling my order.
I wonder if Apple has a shortage of the 32GB ECC RAM modules ?
Surely, Apple will alert us publicly ASAP whether their Intel-based Macs are affected with this Intel
boo-boo. This is such a big concern for all of us, and Apple cannot in good conscience leave us
hanging fire on this.