There is definitely a point of diminishing returns - where that is is hardware, artwork, and process dependent. If you WAY overshoot, you end up with the sluggish problems you reported with such a huge canvas. The printer/spooler can always ignore too much information but when it tries to interpolate missing data you get fuzzy, pixelated images. The best solution is to overshoot your DPI - that is to say build your canvas with more pixels than you end up with printable/displayable dots, but always maintain the aspect ratio (L/W) of the final product. If your design is consumed in other ways (digitally, as a poster/billboard, etc.) then the DPI will likely need to change. So start with your print dimensions, multiply by 300, and that becomes your canvas dimensions.

This would be the BARE MINIMUM canvas size we could use without distortion.

We can make the correlation that dots = pixels, therefore we need a canvas size of (8.5 x 300) by (11 x 300) which gives us 2550x3300. We want to print at 300DPI since this will be hand-held. Let's say we are printing on 8.5x11 paper (borderless) and we want to maximize our drawing view.

Autodesk sketchbook pixel art