Live elusive "Performance bug"

[Maido]

Ok I really hope I can find some light on here, as it seems this "bug" is kinda well known but no one has been quite able to pinpoint it yet.

Intro: running 10.10.1 Yosemite on a mid-2011 3.1ghz i5 with 16mb ram and 828x thunderbolt card

Since a few weeks, I am experiencing heavy crackling on Live even at 60% CPU times, on projects which, previously, ran absolutely fine and smooth with the same CPU occupation.
I tried to reset SMC and PRAM earlier and run ableton from scratch, without any other program, and it ran fine as it used to.
After having worked/played with other programs, I closed them and ran Live again, crackles at low CPU times again.
Rebooting and resetting SMC and PRAM didn't help at all, this time, so it might've as well be total coincidence the first time around.
Here you can find a video showing what I mean:

https://vimeo.com/116287495
Password: abletontest

Keep in mind the song should be 128bpm and without all those crackles

TL;DR: 3 weeks ago, project runs fine and smooth, even at 70% CPU. Now, for some reason, crackles and stuff. Even at 30-40%, I get significant crackles and slowdowns.

What I have tried so far:

- as mentioned, SMC and PRAM reset
- SMC fan control to run all fans to max (just in case CPU was slowing down because too hot? Was worth a shot)
- disconnected ALL peripherals (monitor, 828x thunderbolt card, all usb etc)
- closed all programs, even background ones, even ultra-background ones via activity monitor)
- reset Ableton (=deleted all, all, all preference files, fresh start)
- tried a 9.1.4 version which used to be fine
- removed all VSTs (left a "heavy" one to stress some CPU or testing would've been hard)
- killed the index process into oblivion

I am really out of options, don't quite know what to try anymore. As it is right now, Live is pretty much unusable, since crackles start at 30% sometimes.
Old projects which used to run fine weeks ago are not totally unapproachable.
Considering the amount of money I dumped into this I feel a bit, how to say... frustrated? :p
Already posted a tech support request but posting here too, you never know.

Anyone got any idea? Thanks and much appreciated!

[cids]

Did you install any new software, hardware or driver/software updates?

[Maido]

Nope, no change at all, it literally stopped working right randomly, and I can't get it fixed anymore.
Kinda out of options :/

[cids]

Did you try to increase the latency within Ableton Live? To see if that solves your issues?

[Maido]

I didn't mention my settings as buffer size and so because they are unimportant, as they haven't changed since everything worked fine, and really it went from fine to not fine within 30 minutes. However changing buffer size has no significant impact , it starts stuttering at 40% cpu
I read in some other thread ableton is very much aware of this and calls it the "performance bug", hence the subject, hoped there'd be some update on it

[M-bition]

Did you check at what speeds your cpu-cores are operating ?
Did you check if all cores are being used ?

It is possible they are not operating @ 3.1 Ghz. Maybe your cpu is throtteling for some reason (perhaps heat ?)

[Maido]

Did you check at what speeds your cpu-cores are operating ?
Did you check if all cores are being used ?

It is possible they are not operating @ 3.1 Ghz. Maybe your cpu is throtteling for some reason (perhaps heat ?)

Not sure how to check "real" CPU speed apart form system information one, but if it helps, nothing else slows down on my system, and everything runs at the speed it should run. SMC fan control currently reports a CPU temp of 41C, I have turned all fans to max just to test this out as well.
I am 100% sure the problem is delimited within Ableton itself.

[alpertt]

You said you've tried 9.1.4, same problems with that too?

[Maido]

You said you've tried 9.1.4, same problems with that too?

Yes I actually tried that one too since I had an non-updated copy on my laptop, but no luck.
For now I managed to temporarily put very high buffer size at 44khz and the results are manageable, it's workable at least, I hope some future patch will enhance this.