I can't say, Jody. I would suggest that either holding back at (I believe) the December 2017 level or bringing your system fully up to date are the most viable alternatives. Based on what I've read some of the Meltdown mitigations changed the entire way the operating system is built from sources, so I don't think this is a mix/match type of situation.
I have always kept my critical systems up to date, and have been blessed or lucky to have good, stable operation, but a best case slowdown equivalent to the difference between my computer and one I could have bought for $1,000 less was simply something I couldn't accept.
I wish I could say there was a margin for error here, but I've been through the trial of the latest updates in Win 8.1 not once but twice, (and also with a Windows 7 system) and I really, really measured carefully.
-Noel
P.S., in response to dencorso's note, I found this nice post which identifies the DISM command that can be helpful for removing historically layered telemetry updates:
https://www.askwoody.com/2016/how-to-permanently-remove-kb2952664-and-maybe-speed-up-your-machine-in-the-proceess/