OK! An update,
David, what you said would happen is what happened! All of the exposures at f8, regardless of shutter speed from 1/30 through to 1/250 are 'just right'. All at f11 are slightly under-exposed and all at f5.8 are slightly over exposed. What I get from this is that it is that when using manual flash, aperture guides the exposure, and that shutter speed (unless it is slower or faster than the flash) plays a lesser role.
Art, I'm using the Minolta 280PX which I bought as my first flash unit for my X700. I know that it's not the greatest, but it was bought to go with the x700, and works really well with that camera. It only has two settings for the GNs and so in manual, I have to match the camera's aperture to the distance scale.
FWIW, I am learning a great deal here. As strange as it may sound, using a C220 with a hand-held light meter is really driving home the thought processes necessary to producing a technically decent photograph. I find the whole process of spending a lot of time over one frame very calming and a lot of fun. Compared to 35mm my number of frames is down, but the learning curve is really steep!!!
Thanks again for your continued input everyone!