For a tru SQ system should I shoot for .707 or something else?

[bass_lover1 10+ year member]

Well, your cabin gain won't change the alignment of the sub in the enclosure but it will boost the lower octaves of it giving a different frequency response.

Actually the environment that the setup is installed in DOES have an effect of system alignment, however it will be so minuscule that the average listener will not be able to detect the difference by ear.

Also teamquakecelica 2.0 cubes looks about right for somewhere between .707 so yea your numbers are right.