After further issues with CMP at the beginning of the week, have reverted again to 49922. On checking the size of my userdata folder found it well in excess of 20Gb so whether I hit some sort of ceiling I don't know. However all I had to do was just click on a item in the main CMP window to induce a freeze, having got progressively worse.
I've now limited my downloads to stuff I know would work in 61388 so a route built in 49922 should work in that and by extension, T:ANE.
For those running 61388 it is certainly worth keeping an eye on the amount of stuff you have downloaded and consider a cull if it's getting out of hand - the 20Gb "limit" may vary from user to user.