So my Ncase has arrived today, the good news is my Sapphire 6800XT Nitro+ (L310 W134 H55) can fit in (barely), and not as difficult as I expected, it only took me 5 minutes to adjust the angle.
However, it is not actually 100% fit.
*The cooling module is about 2-3mm longer than the front I/O.
*The bottom of the cooling module is 1-2mm lower than the front I/O because the GPU is a little bit thick.
*Also the GPU is 1mm wider to fit in the case frame.
If you set up the GUP at a normal angle in your motherboard, it will deform the top of the case frame, that you have no way to put the front panel back on.
Or you can adjust 1 degree to let the GUP stuck inside the case frame, which makes the GPU get through the case opening, then you can put back the front panel perfectly.
Now front I/O is actually the most complicated part. Of course you can remove it, but I still want to use the type-C and USB, the meantime I also want the whole build to look perfect.
My way is to remove the front I/O first, then set up the GPU. After setting up the GPU there is a 15-20mm distance between GPU fans and the case bottom, which means there is no way I can put extra fans down there, but space is enough to get the I/O wires to go through. So I put the I/O panel back on, and luckily the front I/O can fit in just like a GPU bracket (1-2mm height error). The front I/O is supporting the edge of the GPU cooling module, it won't hit the GPU fan at all.
The angle of the PCI-E port is slightly off (1-2 degrees), but it doesn't affect the screw on the slot.
And absolutely 90/180 degree GPU power connector needed unless your model cable is soft enough.
I can get into the BIOS and GPU works fine, but I couldn't test more because my SSD still on the way. (Sorry about that)
Overview:
I guess Sapphire 6800XT Nitro+ is the largest GPU that could fit in the Ncase, the dimensions are 1-2mm larger than the maximum proper size. I can manually adjust the tiny gap easily, but still hard to set up or remove.
The official dimension of Sapphire 6800XT Nitro+ is L310 W134 H55, but I have measured as L305-307 W127-135 H50-56 (This GPU is a trapezoid, not a rectangle). So my suggestion is if you gonna put any GPU in the Ncase, the largest dimension shouldn't bigger than L305 W125 H52.