Reply to Traktor 2.6.4 CPU utilization spikes

I hopped from 2.6.1 to 2.6.4.
The CPU utilization meter is in the red most of the time; when opening settings the sound glitches; when I load new track the complete playback gets a few crackels.
And this is with and without CPU multicore support set to on, the time stretching set to low-cpu-speed, windows services killed, no inputs set-up to minimize USB bus load...

The initial tests were done with Audio8 and Audio2. Tuning audio buffers for those, can improve the situation but at that point we are already talking about 20ms+ latency. The Audio2 might be working a bit better since only 4 audio channels are used, opposed to 8 channels on A8.
The granularity of this problem goes down to toggling the mixer filters on or off, switching one FX element from multi-fx to single, not to talk about using key-lock.

When I plug in my Presonus Firebox (with all 8 channels used), all of a sudden cpu utilization is down to 50%. Though I can get it into RED, the sound never stutters.

My CPU is amd athlon ii m320, 2 cores @ 2.1GHz.

Are old NI drivers so poorly written?
Are A6/A10 performing better with new Traktor? (I mostly hear S4 uses with similar complaints, and that's the same generation of soundcards as A2/A4/A10)
Might it be that my CPU just can't take the load? (we all know that multicore utilization is poorly written in traktor)
Is there anything I can do to fix the USB performance? (I have the appropriate filter driver installed already)