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Overclocking is a like a lottery, its not just about the temps, but most of the time is the binning of the silicone, some will go to 5ghz most will not break 4.5ghz, with most able to do around 4.2ghz, but haswell do runs hot when overclocked, so excepting a 4.5ghz oc on Haswell i would invest on very capable cooler, the more you overclock the more you gonna need the fans to spin faster to maintain the temps, the better the cooler the less you going need the fans to rev up to dissipate certain amount of heat, so invest in a very good cooler, with good fans. I would go with twin tower heatsink like Thermalright Silver Arrow SB-E
, its one of the biggest twin tower coolers, even bigger than silver arrow, with two pwm fans (TY141/TY150), you can also go with Extreme edition that comes with 2400rpm fans, but to me its not worth it, as i will never take to those speeds as it will extremely noisy.
Around a $50 budget, i would go with Thermalright HR-02 Macho
, it has been reviewed by SPCR Thermalright HR-02 Macho Quiet/Fanless Cooler
and got the editors choice, you can even add a second fan later on if you feel the need. The problem that i see is your desire of 4.5ghz not sure how the HR02 will handle it with haswell runnign so hot, with that said, seems like Asus AI suite dynamically oveclocks, so temps might not go that high unless a super demanding program like Prime95 stress it. If you with HR02 and R4, i would grab a second Thermalright TY147
and place it on the back of the R4, move the included fan to the front, so you get positive pressure and with the TY147 will end up like push pull with macho, use headers CPU_Fan and CPU_OPT. The fans will look very nice imo as they will match the black/white theme of the R4.
Btw the Fractal Design Define R4 shouldn't have any issues fitting either of the above, as it has a clearance of 170mm, not sure on the NZXT.