Yes, Ozi is way better than Opencpn for planning. For navigation I prefer to print from the Ozi screen the tricky parts, with my route and waypoints in letter size paper. If you fold one side a little, they fit into 1 gal. freezer bags. I keep them handy in the cockpit, and if they are blown away no big deal.

For image conversion (I recall you are a unix/linux guy) I use gimp, it handles almost all the formats.

I remember finding geotiff images from NASA, but I don't have the url. The geo-reference is a lot more accurate than doing it with Ozi, because it covers the projection type, datum, etc.