I've been having a lot of trouble with this lens as the magnification is huge, and you have to be a lot more accurate with the movements between each shot in the stack.
Also a lot of the time my shots are soft and I think I'm suffering from some extraneous light bouncing into lens from my flash setup - so I'm going to have to look into making a shade of some sort (Spotted Rik's in another thread, will use that as a basis for experimentation! - Rik how did you make that stay in place?)
Here's one stack I was reasonably happy with from this setup, common wasp sting. I guess the stinger is 2-3mm long.

Shot with Olympus E330, 4/3->OM adapter, OM Auto bellows, PM-TOB, Olympus 20/3.5, STF-22 Twinflash.
Funnily enough I've been testing out the free demo of Helicon for the last few weeks and this is about the only shot I've managed to get better results with Helicon than CombineZm. It seems to me that for my typical subjects (Hairy wasps and butterflies) at my more normal levels of magnification (2-4:1) CZM does a better job with default settings than Helicon...