Hi, as promised, here are my results.
(KCC only atm, because I could not find the option in calibre)
The official screen resolution of the SONY PRS-T3 should be "758 x 1024 (B x H)" (
http://www.sony.de/product/rd-reader-ebook/prs-t3)
Here's a screenshot how it should look like (converted epub, using calibre viewer)
I did two tests (KCC):
1. using the official specs: 758 x 1024 (B x H)

As you can see, the lower part is missing.
2. using adjusted parameters: 758 x 934 (took about 90 pixel away)

Now it seems to be okay.
Sadly, I don't have the time to figure out the optimal resolution, but i guess this one should be quite fine. If you guys want me to, I can do a deeper research on this one. But do not expect anything from me before Monday evening ^^.
kind regards
PS: Is it possible to create an epub without size limitations, or do I have to stick with pdf for zooming in etc? (for now the comic is displayed correctly via eReader but one cannot zoom in (bad quality). Is there a solution to this problem?)