slow performance and crashes since 5.2

Hi, first post on here. sorry if I should've posted somewhere else or if there's already a thread about this.

Basically since version 5.2 Reaper's performance has slowly gotten worse and worse. As in the same session would start seeing me run out of CPU. At first it wasn't a major problem. But then I would start getting a hang on loading a project. It would get to 'Project loading complete' and just freeze requiring a force quit (I'm on Mac).

So I started opening all my projects in rescue mode with all the FX offline, then selecting all the tracks and toggling FX offline/online. That seemed to work fine and I just accepted the work around thinking I could sort it out when I finished this project. But then even this stopped working. I had to toggle FX online a few tracks at a time and even then somtimes it would hang when doing that. I tried doing save as and removing any plugins I suspected might be causing the problem, only to find that other tracks would then cause the hang. I couldn't narrow it down to a plugin or even too many instances of a plugin.

If I go back to versions of Reaper pre version 5.2 everything runs smoothly and I have plenty of CPU left, whereas I was maxed out before. The problem is that a lot of the work I've done since version 5.2 is corrupted, sections of the arrangement are in the wrong place etc.

I've now been forced to port all my sessions over to Logic as I fear there may come a point where I cannot recover my work.

I'm on a retina MBP 2012. Tried updating to 10.10.5 from 10.9 no change. Tried repairing permissions etc.

Does anyone know if there were performance 'upgrades' that came with 5.2 and if they can be reversed without screwing up my sessions?

Thanks

George

slow performance and crashes since 5.2