I'm seeing suspiciously high cpu with some patches as well. Sometimes I just can't see what could be causing it. 1.6 rarely went above 10% on my machine. In V2, there is an arppaggio patch that uses 60%! Sometimes it's hard to narrow down what's causing the cpu strain. There was one simple patch I had that used 10% with the matrix off, but when I turned the matrix on, it used almost 20% even though nothing was being modulated in the matrix. I feel like maybe something strange is going as far as cpu load. Normally however the mod matrix doesn't add any cpu just by turning it on, that seemed like a special case and now I can't remember what patch it was.
The main cpu strain seems to come from the unison or soft clipping. Keeping the voice count at 3 or less is pretty essential when using unison and it's best to just keep soft clipping off. But even so it seems like sometimes the matrix being on or the cabinet being open can add cpu.