How you gonna post a SM reference without referring to the #1 SM fanboy of this thread (Me)?
Getting that Gyarados analysis onsite was one of the most time consuming things i've ever done. I can actually that in if you'd like (being able to shut down Ferrothorn, Skarmory, etc counts for something)
http://honko.byethost8.com/manly_calc.html
0- SpA Life Orb Gyarados Fire Blast vs. 252 HP / 0 SpD Skarmory in sun: 270-320 (80.83 - 95.8%) -- 56.25% chance to OHKO after Stealth Rock
0- SpA Life Orb Gyarados Fire Blast vs. 252 HP / 168 SpD Ferrothorn in sun: 307-364 (87.21 - 103.4%) -- 56.25% chance to OHKO after Stealth Rock
Remember being able to punch holes is one of the selling points to Offensive DD Gyarados (as you guys said "
it has no trouble punching massive holes early- to mid-game, softening up the opponent's team to the point where another Pokemon can sweep.") and Ferrothorn and Skarmory are very common Gyarados switch-ins.
The drawback is that your main STAB Waterfall is weakened, so either Bounce or Return is left. I like Return as a +1 Life Orb Return does a lot of damage to Rotom-W, another common Gyarados switch-in. Between Earthquake and Stone Edge, I personally prefer Earthquake as I can't stand Stone Edge's miss rate...but I suppose it has its uses (fuck Kyreum-B).