In addition to the 250mm f6.7 Fujinon W and 240mm f9 Germinar-W already mentioned (both excellent lenses), I also highly recommend the 240mm APO Sironar-S. This lens will offer truly outstanding performance, and has enough coverage for most 8x10 applications.

This is an expensive lens - even used, but you didn't mention a budget range. Plus, since you are replacing both a 210mm and 300mm lens, you could use the proceeds from selling those lenses to finance the purchase of used 240mm APO Sironar-S.

Kerry Thalmann
Really Big Cameras