>>18918367252 SpA Choice Specs Adaptability Porygon-Z Boomburst vs. 252 HP / 4 SpD Eviolite Chansey: 300-354 (42.6 - 50.2%)
All considering, it's a pretty decent nuke.
By pretty decent I mean one of two Pokemon in the entire game capable of 2HKOing standard Chansey with an unboosted neutral special move.
The other being this one:
252 SpA Choice Specs Kyogre Water Spout (150 BP) vs. 252 HP / 4 SpD Eviolite Chansey in Rain: 390-460 (55.3 - 65.3%)
It'd make a pretty good nuke.