[Nyara]

Exactly the same stuff as Sunny Day / Fire Blast / Hidden Power Grass / Wing Attack, with just a bit more of raw power on Wing Attack (30+ BP with STAB already added, still not enough to being useful at all), and about SolarBeam, the same calcs adobe about Entei's Fire Blast, but with more raw power, being the most important stuff changing on 3HKO against Vaporeon, Suicune, Tyranitar, and Starmie into 2HKO, so, that could be a buff, but that's pretty much all, if you're really dying for those 2HKO, you can still use Miracle Seed, put Spikes on the field, and damage them just a bit before leaving (maybe with Pursuit).

But even if Moltres had SolarBeam, your opponent will just not switch-in them until it's the turn when Sunny Day ends, and when they do on that moment (not a hard task), Moltres will lost always (bar Critical-Hits). That should be rembered that SolarBeam DOESN'T do more damage even if it's SE in comparison to Fire Blast under the sun and with STAB, it just deals the same, and I already listed the unique OU/BL Pokémon were SolarBeam is more effective than Fire Blast (when Fire Blast is resisted and SolarBeam is SE, or Fire Blast is double resisted and SolarBeam is neutral).

And you're still OHKOing Golem/Rhydon with Hidden Power Grass, and you're still helpless against Kingdra.

Curiosly enough, Drill Peck doesn't deal more damage to anything at all, at least on type-wise and under the sun, Kingdra? SolarBeam deals the same damage. Dragonite? Fire Blast deals the same damage. Fire? Fire Blast deals the same damage. Water? SolarBeam deals more damage. So, Drill Peck doesn't have any use with Sunny Day, outside of the sun, it can be of some uses against Dragonite and Fire pals, but I could rather just use Hidden Power Rock against them, that deals more damage to both. It is not 2HKO against Blissey, and SunnyDay Fire Blast already 2HKO Snorlax (and Drill Peck is not 2HKO, either). Oh, yeah, my error, Moltres' attack stat is lower than it's special attack, so, Drill Peck will do just the 85% of damage than the other options (or just about the same against special walls, and less against physical walls).