I would be interested in what info you have.
On the 7x10, while I could get it to feed, I decided to create a template (Qimage) to use 8.5x11 paper. It had trim lines to cut it down to 7x10 (or any size you want to create). You can pretty much do this for any size envelop you have. Smaller sizes I "two-up".
The reason I liked this better is that the cards could then be created "full bleed"....that is, without any white borders needed. I like the look on this much better. Also, since the cutting is done after the printing, there is no "over spray" or loss of the edge of the image.
Folding without a crease is not a problem. I usually fold the card before final cutting, which ensures all edges match up.
John