So far on 3 VMs where I've checked (all are public facing, on is fairly high traffic MX, the other is a webhost), netstat -s informed me that SACK is barely used.
The bigger impact will be for users far away, with increased risk of packet loss and higher latency.
It's too easy to drop packets with very low MSS and, unless you've got specific needs (someone mentioned IOT), there's no reason to not drop packets with MSS < 536 or so. I believe Window's smallest MTU (MSS + IP and TCP headers) size is 576 bytes for example.