That is an impressive system Bert, can't wait to see first light!
There doesn't appear to many (any?) alternatives for f3 system that can cover a 16803 chip. The closest I can find is the ASA f3 "H" Series, but I'm not sure if they are even in production yet. See this:
http://www.astro-pics.com/31hm.htm (to me the stars at the corners look very average)
Oh and I guess Bert won't want spikes on his stars, especially if he is lining up frames in mosaics.
Terry