Hi Salty,
You can make the image appear to be rectilinear with the Z lens, by careful composition of straight lines. here are a couple of examples done with the 10-17.
The first is what you expect from a FE lens
Pentax *ist DS ,Pentax smc P-DA Fish-Eye 10-17mm F3.5-4.5 ED (IF)
1/20s f/3.5 at 10.0mm iso1600
This next one is not Defished. Taken a few moments after the first. It is just the way it was composed. I was rather surprised by this at first.
Pentax *ist DS ,Pentax smc P-DA Fish-Eye 10-17mm F3.5-4.5 ED (IF) 1/25s f/3.5 at 10.0mm iso1600