That sounds like you were running into the problems Chris made me aware of. If you were, the speed improvements in the release will be dramatic!

What was happening (ever since AE CS6 and before!) is that when you had an EXR sequence and AE was running EXtractoR or something, AE would read the EXR header many, many times—once for each channel, in each instance of EXtractoR. When you add in Cryptomatte the EXR header gets much bigger, multiplying the problem. The result was that these EXR sequences could be unbearably slow. For some reason AE didn't do this when you just had a single frame.

The latest release of AE is still doing this, I believe, but this version of the OpenEXR plug-in always caches channels and also headers. This makes things much better, as I think Chris will attest.

Now, Cryptomatte is still not the fastest thing. After all, it usually processes 12 EXR channels in one pass. Some proxy creating might be wise.

But the extreme slowdown there was before should now be gone.

Brendan