I've been using TurboPrint for ages and got the 7.50 update after switching from an Epson Stylus Colour 850 (couldn't clean the head any further and still got stripes) to an Canon i950. I've been printing A4 borderless photos at 4800x1200 dpi and the quality is impressive. You need to have the right settings (and paper) though. Also, I found some bugs (concerning TrueMatch and high resolutions), but Florian Zeiler immediately fixed them and sent me a new version.
TurboPrint supports a lot of different dithering patterns -- I've always been using the Super-Error-Diffusion with excellent results. No black dots whatsoever. The only way I think you could be getting these black dots would probably be a "wrong" value in the Truematch UCR settings.
AFAIK the PPC dithering routines only work under PowerUP. Anyway, the TP7.50 binaries seem to work nicely under MorphOS aswell -- and then it's really fast enough
Also, the Epson ESCTool coming with TurboPrint is a third party contribution and if you have read the docs, the ink level display has never been implemented. Nothing to blame IrseeSoft for.
I never found GraphicsPublisher unstable except for the ASL Font Requester, which seems to be unstable on my machine per se.
In general, I am very satisfied with TP and I am happy that the Amiga is still supported by IrseeSoft, despite the poor revenues.
