Doogie, i have a bust Pace RC200F3 and an RC300, both are 18" as stamped on the bottom bracket.
However the old F3 is quite a bit smaller than the 300. I measured F3`s bb centre to top tube centre to be 15.5 -16" and centre to top of seatclamp is only around the 17" mark. My 300 I don`t have with me at the moment but it`s definatly bigger, I know it is exactly the same measurements as my friends RC200F6 18".
So who knows?