Well the i3 you are considering is similar to i3 i have on my download station just mine is limited by its clocks, but on the Sandy Bridge and Haswell downclock both to 800mhz on idle both produce very little heat. I have been running mine on HR02 (original, not the macho) + TY140 for over 2 years (its basically the same combo as the macho). Now the weakness of this combo is the fan, not that its bad, imo its pretty decent, but to me its that most of the time i have only been able to run it at 700rpm, i did try 600rpm but the fan ticked, for the average user its fine, and probably its even better that doesnt drop as low, and most dont buy the macho for it being super quiet, but the biggest reason is the cost/cooling, its simply one of the best cooler for the money atm. The HR02 comes the intention of creating a passive cooler, the HR01 was sold without a fan, the HR02 was also sold without a fan, and now the HR22 is sold without a fan, but the macho does much better with a low rpm fan than fanless.
My guess is with a very low rpm the Macho would do better than the Mugen 4, as its going more into the fanless territory, were the more area and widder spacing should give the edge to the HR02, a fan like Noctua NF-A15 PWM is ideal imo, as its a very big controllable range, from 200rpm to 1500rpm, compared to TY140 600-1200, the fan are very similar on the body, size, position of the holes, etc, it will work out fine with the included clips that it comes.
I feel this is the quietest combo you can get for the best cooling at very low rpms, but the problem is you going to need a motherboard that can manage the NF-A15 PWM
, a lot have restrictions on the bios into the minimums pwm % you can drop off (like ASUS ROG), a lot have crappy software, some might not work with speedfan by not able to recognize the sensors, etc. MSI bios and Asus FanXpert2 both can deal very well with the fan, thats the two experiences that i have, Intel is also pretty decent on pure bios, AsRock seems also to have good fan management on pure bios (but i haven't tested it to know for sure), not sure how is gigabyte.