Ah! Thank you. It of course makes sense about the extra operations to use an integer. I suspect a "float" will be much worse, but not tested yet! Now I understand why a short piece of code using a float, is so much bigger than using integers in much longer code. A valuable lesson indeed.
FWIW, majenko's comment made me wonder if anyone had attached a FPU coprocessor to an Arduino. A quick Google search for "Arduino fpu" found this in the playground: http://playground.arduino.cc/code/fpuSo it's there if anyone really wants to play with it.