I have the ARC TMIC and have noticed that due to the design of the core being different i.e. bigger vanes and less number of fin lines the heat is not stored as much as the standard.
I ran from Liverpool to Manchester at 07:30am so stuck in traffic, got to work, stood the car running for a few mins, popped the bonnet and felt the TMIC, it was only slightly warm, were the standard TMIC would be scorching.
I think the performance gains are seen purely due to the ability of the air able to pass through the ARC compared to the standard.
I measured the dims of the ARC and compared them to the standard and found there to be negligable difference, so imho the performance lies in the acceptance of the ARC to pass the flowing air.
Ant.