When googling for something I stumbled upon this thread I started few years ago.
So I would like to add few comments in case anyone else is asking the same question and stumbles upon this thread. In a nutshell - if you have a perfect case already in mind and only problem with it is that it lacks the handle - just add it. For vast majority of cases this is quite trivial and involves only drilling few holes and bolting the handle to the case. Second comment - be mindful of the weight. If possible try to stay under 12 ... 15 kg. After that weight every extra kg adds an considerable amount of uncomfort for lugging one around. If you go above approx 16 kg I would strongly suggest adding also a shoulder strap.
By now I have gone through a number of iterations with my quest for a "perfect" portable case.
(1) CM Storm Scout - heavy steel case which just happens to have an handle. Did not really like it - far too heavy, did not take long gfx cards.
(2) "Soliton" - Revoltec Fifty 3 with heavy mods - Nova 1080 monster radiator, HDD and SSD hotswap bays, very tight packing - but .. it was heavy and I needed more room. Total weight 23 kg. In retrospective it was pretty decent but could have been a bit more rigid. It's the green one in above pictures.
(3) "Soliton stretcher" - the black EATX case from above pictures, same nova 1080 rad, 3 gfx cards, hotswap bays - disregarding the question of weight altogheter bcos of POWEEEER ... but apparently 32 kg is enough to leave bruises on ones shoulder even with the shoulder strap - it had to go eventually - mainly because of weight. It was a server chassis made of 1mm steel so the dry weight alone was like 16 kg or so.
(4) "Kohver v.3" - Some modded sharkoon case, the other end of spectrum, 12.5 kg strictly air cooled, no hotswap bays - making it all as light as possible. Served me fine until I got 390X but it was such a howler in that case that wife walked up from the first floor from watching the TV to see what is making such howling when I put it in and started gaming. So I had to watercool that thing and, unfortunately, that meant some added weight and again a new case. It had also some issues with rigidness and construction quality - had to mod a displayport cable to be able to plug it into 390X in the top slot bcos some edge of the case was apparently not strictly following the ATX spec.
(5) "Kohver v.4" - Some ancient aluminium case from ebay with heavy mods including new lasercut front panel, reinforcement plate for handle, etc. To be honest if not the horrible howling of 390X I would probably be still on the previous iteration. But the new one is better now that I have done it - much better airflow and CPU is sitting at ~75 C under load compared to hitting as high as 90C on hot days in the Kohver v.3. I did not consider price anymore really when picking a case for Kohver v.4 - LianLi, MountainMods, anything was on table as long as it would fit what I'm looking for exactly ... and none of them did so I had to mod. With laser cutting, painting and everything I ended up in the same price ballpark as these mentioned plus ungodly amounts of elbow grease. If you find a case that hits the tickboxses just go for it even if its a 300+ EUR one - it will be cheaper than what you will end up if you have to do a proper mod if you count your work-hours price fairly. But when you will have to rebuild the case anyway then it no longer really matter that much with what are you starting with as what was there in the beginning will not be what you will have once you finish with it.