Tom, if you can find a smooth surfaced paper that will hold the cyanotype well (both the sensitizer and the final Prussian blue pigment), and won't roughen with repeated wetting and drying, a cyanotype is capable of holding as much detail as a silver gelatin contact print. The best I've done was on Canson Montval "Rough" (which is a lot smoother than other cold pressed watercolor papers I've tried), but I'm still looking for a smoother surfaced, "harder" paper that has the same resistance to wetting as this reinforced watercolor paper. I'm tempted to try plain old posterboard -- it's certainly cheap enough to experiment on.

BTW, you can also tone cyanotype in strong, cold tea or tannic acid, either after bleaching in sodium carbonate solution, household ammonia solution, or without bleaching, to obtain a range of final colors from an orange-red to near-neutral black, while the paper will stain slightly and range from barely off white to a distinctly tan shade. This can open the process up for subjects that might not be at their best with a blue-toned print (like portraits -- lots of folks dislike portraits in cyanotype, but with tea toning they can look very much like matte-finish silver gelatin prints on an ivory- or buff-toned base -- a very good look for a portrait).