I don't know OGL very well either. However, when I looked through the code last year I convinced myself DX driver uses Auto Texture Management and I couldn't see an equivalent for OGL. I wasn't that fussed with OGL at the time but, if I HAD been, I would have concluded it either doesn't do texture management or does it by default. I would then have searched (probably gamedev.net first) and found the OGL article on Gamasutra. I would then have convinced myself OGL does it by default and left it at that.
***IF*** I was still not happy with the response I would have posted exactly as you have and asked for feedback.
Here is the results from my T61 (372.23mb VRAM)
Test1 : OGL stabilises at 100mb VRAM usage.
DX uses 356Mb of VRAM.
In both cases the image disappears when I move the mouse.
Test2 : OGL uses 6Mb of VRAM and displays white rectangle.
DX used 52Mb of VRAM and image disappears when mouse it moved.
Test3 : OGL uses 12mb of VRAM and image disappears.
DX uses 52Mb of VRAM and image disappears.
If I was testing this in anger I would check my drivers and/or conclude that my Graphics card is rubbish.
***IF*** I was still not happy with the response I would have posted exactly as you have and asked for feedback.
Here is the results from my T61 (372.23mb VRAM)
Test1 : OGL stabilises at 100mb VRAM usage.
DX uses 356Mb of VRAM.
In both cases the image disappears when I move the mouse.
Test2 : OGL uses 6Mb of VRAM and displays white rectangle.
DX used 52Mb of VRAM and image disappears when mouse it moved.
Test3 : OGL uses 12mb of VRAM and image disappears.
DX uses 52Mb of VRAM and image disappears.
If I was testing this in anger I would check my drivers and/or conclude that my Graphics card is rubbish.