Don't forget the bracket and power button are still there. This is what the new one looks like:
You can see that it's really the power button PCB and connector that are the limiting factor here.
The difference in length restriction is ~299mm at the limit without the front I/O, 294-290mm with depending where you measure from and how much wiggle room your GPU allows for the cables at the front:
Height is not affected by the I/O module at all, but by the chassis. That said, I've eliminated the two clips at the front and rear that were right in line with the GPU PCB, so that should help somewhat with tall GPUs.