I have a Silhouette machine, but I found quite the opposite of what Beth found: that it wouldn't cut through even thin acetate, even at the highest settings. (I may have a different model than Beth, but the Silhouette folks told me they don't have a food-safe - or non-food-safe - acetate that they recommend for their machines either.) So upon recommendation of another cookier who sells stencils, I invested in stronger die. I have yet to try them in the machine. My first experience with it was very frustrating.
I'm looking for a stencil machine as well. Since you say that you invested in stronger one, can you tell which one would be a good choice?
I didn't invest in a new machine; I invested in a stronger die (the cutting mechanism) for it. I honestly haven't had a chance to test it yet (yes, I'm that backed up with work), so I can't tell you if it was any better. Sorry. I've been using stencils cut by others lately, because I was so frustrated with my machine.