Ok. did a little more digging. So.
1) In trying to make an example project I can confirm that there is always black screen after default loader as layout images are loaded into gfx memory.
2) However, this black screen time is acceptably small, fraction a second on a fast machine, even if I am loading in 30 large images ranging from 1000x1000 to 3000x3000 in size, looks like it is hitting around 300mb gfx memory.
3) but my game seems to be loading in over 1.3GB for the layout. which seems a excessive for what Im doing so it looks like I may have some legacy large images in there that have been overlooked.
So I will have a dig around my project to see what is causing the large gfx load
but yea definitely looks like there is black screen during gfx load which will be obvious with large games on slow machines so I may raise a bug for that.