One thing to keep in mind is that the 7800's pixels are not square like you have them (unless you are using 320 mode, then all of the cool color modes that GroovyBee mentioned above will unfortunately go out the window)
I'm trying to remember off-hand if the 7800's pixels are twice as wide as they are tall, or something like 1.5 times as wide as they are tall.
If you're going to stick with 160B - which I also recommend, you might want to adjust your bitmaps to reflect that.
Bob