mellow37

The Meshify S2 will solve those GPU length problems.  Or if you really like RGB I'd look into the Define S2 Vision RGB.  That should still have better thermals than your NZXT case.
 
Oh, and no need to worry about your AIO, you can always attach the radiator to the rear of the RGB fans.  You'll just have a little less illumination from the inside.

It doesnt matter. Most people put the fans pushing air through the rad just for the aesthetics since most fans have LED lights now. Performance wise makes almost no difference. 
 
To throw in another case, Phanteks Enthoo Pro M TG is a slightly longer Meshify C, and can hold a 280 or 360 rad at the top for $99 USD. 

I had an NZXT H500i and the airflow was terrible, I switched to the Fractal Design Meshify C and have never seen better thermals it's absolutely wonderful. I have also built in both the Coolermaster H500m and the Corsair Obsidian 500D. My top 3 cases are the Fractal Design Meshify C, Fractal Design Meshify S2, and the CoolerMaster H500P. The Corsair Obsidian is a beautiful case but like the NZXT H series line of cases it is very restricted it looks like it isn't but it is, only has a few slits in between the tempered glass and the frame to supply air to the front fans. The H500M however like it's H500p counterpart has a mostly mesh front panel for air intake and two large intake fans. Personally if you're looking for a high airflow case, anything with a mesh front panel and top mounting rad support is the way to go as mounting the Radiator in the front for intake will greatly restrict thermals. My new check list for cases is a Mesh front panel, two to three intake fans, 240mm+ top rad support and of course a nice tempered glass side panel.

Thank you for the replies @NumLock21 and @SpookyCitrus. The MB511 looks quite nice, but it does indeed not support a top 280 AIO.
 
When I was planning this build I looked into the Meshify C but it is shorter than NZXT H500 and my GPU would probably not fit after I install the AIO at the front. The CM H500p actually has terrible reviews but I guess you are referring to the updated Mesh version which does have excellent airflow. Between the CM H500, CM H500P Mesh and CM H500M (ordered by price) only the last one is available anywhere in my country and even though it is expensive I am ready to spend that money and keep my parts cool.
 
On a side note, if I go with the Cooler Master H500M and mount the AIO at the top, should I have the fans under the rad pushing air out, or on top of it pulling it out?