Sorry it took me so long to notice this. I'm fairly sure that the old Silhouette SD, the old Cameo, and the new Cameo do not have much, if any difference in their cutting ability. I have the SD, on which I started, and a Cameo that I bought for about $250 in the middle of last year. The SD cut only 8" wide; the Cameos 12", which is a big difference when laying out N scale buildings.
One difference between the Cameos might be the dialed cutter head, which allows you to cut deeper--I think they were on the older Cameo, but are standard on the new. The head will fit on all three models. This cutter head allows you to extend the blade much further than the 0.3 mm of the old SD. You will need it to cut even .015 " (0.375 mm) styrene, let alone .020" (0.5 mm). With a new blade, the Cameo will just barely cut through .015; with .020 you are into the score and snap technique, as well as making interior openings with an "X" scored in the opening to help you break them out. With either thickness I cut with the blade extended to the maximum--it seems necessary to cut all the way through even on .015.
I graduated to a larger BlackCat Cougar about 2.5 years ago. It will cut through .020 (with the blade extended far past recommendations). Styrene has so much drag that you do not want the cutter head as close to the material as recommended. No matter how much stick-um you put on a cutting mat, the styrene will tend to buckle.
In any case, you will be using multiple passes at a slow speed if you want the blade to stay on track. Too much cutting force, and the blade will start to wander in one direction or the other, even on the Blackcat. With the blade extended 1.0 mm for .015 (0.375 mm) styrene, I have to use maximum force on the Silhouette, and half pressure or less with the BlackCat. I am at about 1/3 max speed (perhaps 3 cm/sec for the Cameo), and 11.5 cm/sec on the BlackCat, which can reach 800.
I simply wore out the SD because cutting styrene is really pushing its limits; the Cameo replaced it, and I use both the Cameo (for prototyping and quick simple cuts like rectangles) and the BlackCat (for production or anything with a lot of windows and doors). Now, I'm cutting every day and sometimes all day; in hobby use, the Cameo will last much longer.
I should mention that I do not use a cutting mat for styrene on the Cameo nor on the SD.
I should also say that cutting styrene seems more an art than a science, as every batch of styrene sheets I buy requires different settings. I buy 10-20 4' x 8' sheets at a time.
