David,
I have no particular experience in shooting races, but my 0,02 $ on further
equipment are:
A FM2n is a very nice camera as a second body. It is in the same price range
as the N70 and will give you serveral features AF-Bodies don't have:
* You are independent from temperature and battery-consumption, as the FM2
needs only few power and a spare battery is easy to carry
* Sometimes I have the need for manual winding, like shooting concerts. I
once did a shooting with my F601 and it wound directly after firing -
disturbing a moment of silence within the singing
* The FM2 is very rugged and compact.
OTOH getting a N90s or F100 will give some other nice to have features like
vertical grip, AF- and winding speed and using rechargebles. But these
bodies are more expensive then a MF-Fm2.
Hope this helps - Martin