The speed of the CF Express cards should be quite satisfactory, the CFast 2.0 cards in the 1 DX Mk II were quite a bit faster than the fastest Compact Flash cards ever made and the CF Express cards at the even newer faster cards. So I ordered one of the Sandisk readers, and one of the Unitek readers - they should be here by Saturday.

Thanks @Chris for your promopt reply

I agree the RF F 4.0 70-200 is very appealing - small, light, very sharp I am certain, and enough cheaper than the f2.8 version to be much easier to purchase.

Just an added side note - both of the R5s I received yesterday are firmware version 1.1.1, which is the latest current version from the website, I believe. I was happy to see they did not need immediate firmware improvements.