Alright, since DT isn't here, I'll use his tiers for him: (Actually, once you get the hang of them, they're rather handy.)
Specs Gyarados:
On average OHKOs with super-effectives the following:
Sdef teir 113.19 (Dragontamer's tiers) and below, like the amazing:
- ~Min-sdef/hp primpate! (Ooh, goodie!)
- ~Min-sdef/hp Skarmory, actually. Most don't run min hp/sdef, though
- ~ macargo, regardless of sdef/hp
- ~Yanmega, min hp/sdef
- ~Rhydon
- ~Nosepass
- ~Honchkrow min hp/sdef
On-average 2HKO with super-effectives of note are the following:
- Max HP/sdefSkarmory: Actually, that's still pretty good if you catch it on the switch
- Max HP/sdef carnivine!
- Gliscor with max sdef-stats/hp
- Max hp/sdef honchkrow
- Max sdef-hp steelix.
Alright, you get the point. This set would do WONDERFUL in UU (which gyarados is definitely not), but otherwise, it's not all that useful, unless your entire goal in life is killing their skarmory, which, whilethough a wonderful thing, can be done by other pokes much more easily, with much more versatility.
Nice try, but like I said, save it for UU and make the lame excuse that it came from magikarp, so it can't be THAT good.
I hope this hasn't shattered your dreams. Oh yeah, somebody asked about cress... It's not even a 6hko, not including moonlight or leftovers, or the fact that charge-beam will kill you on turn 2 or 3.
And yeah, a couple of the numbers are off, but they are close-enough to give the counter-argument to this set substance.