Maybe I said that wrong let me be less clear and more to the point lol
I have my doubts about any 45 mm rad being only 1 watt behind any 60 mm rad when you compare apples to apples that is to say 120 vs 120 140 vs 140 360 vs 360 or 420 vs 420. The physics make no sense.
I have a UT60 420 in the top had no problems installing, I have 10mm clearance to HS on mobo, 20mm to memory clearance no problems removing a fan for greater access to mobo screws, I placed the 420 as far forward as possible and it's not in the way of the 8pin eps at all and I'd venture to say the same is true with most mobo that don't have the EPS in the middle top of the board (poor choice by Asus), and I'll take UT60 420 over a XT45 420 any day of the week.
There may be little difference between a 480 and 420 according to the calculator you are using but the XT45-420 has approx 810,000 less sq mm of mass than a UT60-480
480*120*60=3456000 sq mm
420*140*45=2646000 sq mm
I know that's overly simplistic and actual surface area may vary a bit due to FPI etc but still hard to think it only a little bigger.
It's not hard to figure out if utilized properly (right fans) which one would perform better and me still thinks the difference is more than 1 watt.
Of course all this assumes both configs are in push/pull and both are using the highest quality fans at medium to low speed putting both configs on an even playing field.
If you use previous gen 140mm fans the 420 would be at a disadvantage similarly most assume a trade off when using a 60mm vs 45mm radiator. The 60 can only use push or pull and the 45 can be configured using push/pull in other cases where folks have measured the difference. If that is assumed and used for the calculation the 420 again would be at a disadvantage. Furthermore most evaluations I've seen for comparison to 120 rads use 1st generation high restriction 420 rads like the swiftech. Such is not the case with the Enthoo Primo Case, the Phanteks PH-140SP fans and the Alphacool UT60 420 rad there is no such limitation.
Bottom line when you couple three factors
1) the enthoo primo case ability to accommodate 140mm rads
2) the latest gen 140mm fans with static pressure equaling that of high pressure 120mm fans
3) latest gen 420 rads with flow rates equaling that of there 120 rad counterparts
The game has been changed in favor of the 140mm rads and all that you read contrary to this maybe wrong IMHO