I just pushed v. 1.41, GUI is still in development but I added a bunch of optimizations from proDOOMman and Birua forks (white border cropping, page numbering removal) and some other stuff like autocontrast, image centering (images are now fitted and centered into device's native resolution) and some command line options to control how to preprocess images (e.g. if you want to upscale or stretch images).
You'll find last version on github
as always, check it out and give me some feedback!
PS: every feedback for Paperwhite is appreciated, ATM I don't own one anymore and I'm testing on my K3!