The power of AC should be equal to power used (=heat produced) by miners.
Without actually forcing hot air out, we talking (1250w*4)+ (3200w), which will require a very huge air-con system, which is a bad idea IMO.
Use a Y duct with an incline duct fan, and rest assured that the AC hole won't be large enough, the standard hole saw we use here is 6.5cm, you will need to widen it by a lot.