Actually is has been in "show room" and has only cover the 700mi. since June of 2001. Don't know about the F40 vs. the GTO purchase, I believe the GTO project was started when the prices were out in the stratosphere. The F40 is a more recent acquisition. Acutally the price of Ferraris are pretty ridiculous regardless of the model, in every case (as this one) it is a hedonsitic exercise!
Engine mods are considerable, including, new block and 4 valve head, JE piston, custon crank, twin turbo with air to water intercoolers, Motec engine management, Porsche 996 gearbox. 590hp is using pump gas and 16psi, at 22psi and race fuel you are looking at over 700 hp (sic). Not that one would need that kind of power.. but if you added nitrous...just kidding!