Hi there,
first thing to know, post-op or not, that any gg's depth is not much more then ~4". BUT, the big but, - this will go OK to twice that when aroused i.e. ~8". Same incidentally applies to width.
We mostly, would struggle to get 38mm width, ggs will quite easily go to 60mm and giving birth dilating to 100mm is pretty much the norm.
For this reason it is a good thing to get as much depth as one can, say 6 - 7" at best. More seems unrealistic.
Next, - it depends on technique and ALSO on available skin and skin graft 'material'.
If circumcised there is obviously less to work with, it may also result in less depth.
If all fails, there is colon-section (colovaginoplasty) which quite easily can provide 8" depth but will result in a much more invasive operation, leaving a scar about 3x the size a hysterectomy or c-section would leave.
I've seen my one friend after her colon-section (the only option in SA's GRS protocol)
I hope this helps,
Axelle