You cannot turn the HUD off in prologue. I'd really like to do this, I'd even make it obligatory for online races I'd host if I couldThe HUD may be in "simple" mode. You could do the same thing in GT4, where the position would only show up at sector lines and the S/F. Though in GT4 this would also get rid of the gear suggestion.
Is that option available in Prologue? If so, what effect does it have on the HUD?