Best radiator air flow configuration for my case?

[vinnas]

OK, this is pretty much driving me crazy. I've been searching arround the web for hours now and people are obviously divided about this topic. My case is a DS Cube, and for those who aren't familiar with it, it only has a 200mm fan on front as intake and a 140mm one on the back as outake (i'm using aftermarket fans with higher airflow on both) and space for 2 fans or radiator on top. Recently i acquired and installed a Nepton 240M on the top of the case, taking air from the inside of the case and blowing it out, as i didnt want the CPU heat to be blown directly into the other components, also the fact that hot air always goes up, basic physics. I did think though, that the fact i'm getting air which is at least a bit hotter than the outside air will impact the CPU cooling performance, and honestly i'm not getting very good results as it is. Testing with AIDA64, i'm getting idle temperatures of 40º and under load stress test, about 70º to 74º for the CPU as a whole, but with some specific cores achieving up to 90º. I honestly expected for it to be better since the water cooler itself is not faulty in any way (i also overclocked a little bit my i5 4690 from 3.5GHz to arround 4GHz, but i don't think thats enough to justify that bad cooling performance). So here's the big question, in my specific scenario, considering all the aforementioned, my PC case and it's limitations, is my actual setup the optimal? I'm tired of people fighting over "rad as intakes are better" or "rads as outakes are better", i know theres pros and cons to both, but i need to know the best for my specific scenario. I don't know if the 140mm fan on the back is enough to exhaust so much heat coming from the components and the rad, but i do know that CPU temperatures would probably be better if i used it as intake. I want a good airflow general scenario, meeting the best cooling options. Thanks in advance!

[JebKerman]

I'd have the rad exhausting out the top, and both the front and back fans as intakes. It should give you the best of both worlds, though getting good airflow in a case like the DS is not easy (and I've got the big ATX brother of your case).