I assume your referring to .40 cal., correct?
Every firearm is different, but I usually go with the OAL that fits the magazine and chamber without getting into the lands, and that provides enough neck tension.
I seat the 165 gr. G.D. for the XDM at 1.130", which is .005" longer than Speer used during testing.
I just read your question again, and realized you may be asking how long is the Gold Dot bullet, is that correct? Or are you asking about the OAL used by Speer or another publisher?
GS
Quickload says it's .560" long. Maybe someone can measure one and verify that.
Check out JBMballistics.com.
I just loaded a box of those, and if memory serves me correct, I believe they're a hollow base. This may be one of the reasons for greater internal case volume, as you suggested.
GS