Donald good luck with a point light source. It is a very demanding light source with which to work. The system I have while easily centered etc still is extremely demanding of cleanliness and negative defects.
It is true that my work is mainly 35mm and the magnification (typically 6.5x) is such that extremely small dust motes are rendered with clarity and are much helped with oil immersion. The converse, if using a 5x7, is the magnification is much reduced but the area to be kept cleaned is 20x more and it may well be as much of a head ache. I am inclinded to think that anyone regularly using a point light source for enlarging would be well advised to have a closed off negative loanding/printing station that is a high air pressure are and is fed with air that is cleaned thru filtration by a laminar flow.
But, Don I guess you will have to find out for yourself.