Well, just for the heck of it I went ahead and enabled encryption on the SDCard. I didn't notice any performance differences, but I wasn't running any SDCard benchmarks or transferring large amounts of data to/from the SDCard so I can't offer any useful data there.
However, I do have some input on this matter:
1. Enabling encryption requires you to use a password lock screen (not swipe, face, pattern or PIN) - it has to be 8 characters including one number
2. This means that if you're frequently turning the screen on, or have a very short screen timeout, you're going to be constantly having to input the password
3. If you connect the phone to a computer via USB, the MTP connection won't work until you input the password on the phone
4. If you remove the SDCard from the phone and put it in an adapter connected to a PC, it seems like it's not recognized at all (I've got to recheck this since my external adapter has been acting up)
Overall, since I access my phone rather frequently, it's been a hassle dealing with the password, so I'll probably turn encryption off once I'm done experimenting.
Sent from my rooted, debloated, deodexed Sinclair ZX-80 running CM -0.001 using Tapatalk 2