I decided I'd write down all the relevant special attacks and their strengths. The most important ones are bolded. Note that some attacks are omitted due to sharing Special and Base Power with another attack (e.g. Birds' and Eeveelutions' STAB moves); I have not omitted the one case I found of two attacks having identical power due to Base Power and Special differences cancelling out exactly.
There are also some NHKO cutoffs for the four most relevant neutral (or neutral-ish) targets.
Slowbro's +6 Surf: 141930
---possible OHKO on Snorlax--- (141414)
---possible OHKO on Alakazam--- (136248, non-Psychic)
Slowbro's +6 Psychic: 134460
---possible 2HKO on Chansey (128333)
Mewtwo's +4 Blizzard: 119520
---guaranteed OHKO on Tauros--- (115883)
Slowbro's +4 Surf: 110010
Mewtwo's +2 Psychic: 109620
Snorlax's +6 Blizzard: 109440
Slowbro's +4 Psychic: 104220
---guaranteed 3HKO on Chansey--- (100394)
---possible OHKO on Tauros--- (98614)
Mewtwo's +2 Blizzard: 97440
Mewtwo's +4 Ice Beam: 94620
Snorlax's +6 Ice Beam: 86640
---possible 3HKO on Chansey--- (85433)
---guaranteed 2HKO on Snorlax--- (82930)
Snorlax's +4 Blizzard: 82080
---guaranteed 2HKO on Alakazam--- (79796, non-Psychic)
Mewtwo's +2 Ice Beam: 77140
Slowbro's +2 Surf: 73530
---possible 2HKO on Snorlax--- (70751)
Slowbro's +2 Psychic: 69660
---possible 2HKO on Alakazam--- (67905, non-Psychic)
Snorlax's +4 Ice Beam: 64980
Zapdos' Thunder: 62640
---guaranteed 2HKO on Tauros--- (57776)
Jolteon's Thunder: 56880
---guaranteed 3HKO on Snorlax--- (55180)
Snorlax's +2 Blizzard: 54720
Mewtwo's Psychic: 54540
Starmie's Hydro Pump: 53280
---guaranteed 3HKO on Alakazam--- (53026, non-Psychic)
Lapras' Blizzard: 51840
Kingler's Crabhammer: 51660
Alakazam's Psychic: 49680
Zapdos' Thunderbolt: 49590
---possible 2HKO on Tauros--- (49167)
Mewtwo's Blizzard: 48480
Cloyster's Blizzard: 48240
Victreebel's Razor Leaf:47677
Exeggutor's Psychic: 46980
---possible 3HKO on Snorlax--- (46957)
---posssible 3HKO on Alakazam--- (45124, non-Psychic)
Jolteon's Thunderbolt: 45030
Hypno's Psychic: 44280
Snorlax's +2 Ice Beam: 43320
Starmie's Surf: 42180
---guaranteed 4HKO on Snorlax--- (41146)
Starmie's Psychic: 39960
Jynx's Psychic: 38880
Mewtwo's Ice Beam: 38380
---guaranteed 3HKO on Tauros--- (38298)
Chansey's Blizzard: 36720
Slowbro's Surf: 36480
Starmie's Blizzard: 35520
---possible 4HKO on Snorlax--- (35014)
Slowbro's Psychic: 34560
Gengar's Thunderbolt: 33820
---possible 3HKO on Tauros--- (32590)
Gengar's Psychic: 32040
Chansey's Ice Beam: 29070
Tauros' Blizzard: 28320
Starmie's Thunderbolt: 28120
Snorlax's Blizzard: 27360
Lapras' Thunderbolt: 27360
Golem's Fire Blast: 24960
Tauros' Thunderbolt: 22420
Snorlax's Ice Beam: 21660
Exeggutor's Mega Drain: 20880
Gengar's Mega Drain: 14240
There are also some NHKO cutoffs for the four most relevant neutral (or neutral-ish) targets.
Slowbro's +6 Surf: 141930
---possible OHKO on Snorlax--- (141414)
---possible OHKO on Alakazam--- (136248, non-Psychic)
Slowbro's +6 Psychic: 134460
---possible 2HKO on Chansey (128333)
Mewtwo's +4 Blizzard: 119520
---guaranteed OHKO on Tauros--- (115883)
Slowbro's +4 Surf: 110010
Mewtwo's +2 Psychic: 109620
Snorlax's +6 Blizzard: 109440
Slowbro's +4 Psychic: 104220
---guaranteed 3HKO on Chansey--- (100394)
---possible OHKO on Tauros--- (98614)
Mewtwo's +2 Blizzard: 97440
Mewtwo's +4 Ice Beam: 94620
Snorlax's +6 Ice Beam: 86640
---possible 3HKO on Chansey--- (85433)
---guaranteed 2HKO on Snorlax--- (82930)
Snorlax's +4 Blizzard: 82080
---guaranteed 2HKO on Alakazam--- (79796, non-Psychic)
Mewtwo's +2 Ice Beam: 77140
Slowbro's +2 Surf: 73530
---possible 2HKO on Snorlax--- (70751)
Slowbro's +2 Psychic: 69660
---possible 2HKO on Alakazam--- (67905, non-Psychic)
Snorlax's +4 Ice Beam: 64980
Zapdos' Thunder: 62640
---guaranteed 2HKO on Tauros--- (57776)
Jolteon's Thunder: 56880
---guaranteed 3HKO on Snorlax--- (55180)
Snorlax's +2 Blizzard: 54720
Mewtwo's Psychic: 54540
Starmie's Hydro Pump: 53280
---guaranteed 3HKO on Alakazam--- (53026, non-Psychic)
Lapras' Blizzard: 51840
Kingler's Crabhammer: 51660
Alakazam's Psychic: 49680
Zapdos' Thunderbolt: 49590
---possible 2HKO on Tauros--- (49167)
Mewtwo's Blizzard: 48480
Cloyster's Blizzard: 48240
Victreebel's Razor Leaf:47677
Exeggutor's Psychic: 46980
---possible 3HKO on Snorlax--- (46957)
---posssible 3HKO on Alakazam--- (45124, non-Psychic)
Jolteon's Thunderbolt: 45030
Hypno's Psychic: 44280
Snorlax's +2 Ice Beam: 43320
Starmie's Surf: 42180
---guaranteed 4HKO on Snorlax--- (41146)
Starmie's Psychic: 39960
Jynx's Psychic: 38880
Mewtwo's Ice Beam: 38380
---guaranteed 3HKO on Tauros--- (38298)
Chansey's Blizzard: 36720
Slowbro's Surf: 36480
Starmie's Blizzard: 35520
---possible 4HKO on Snorlax--- (35014)
Slowbro's Psychic: 34560
Gengar's Thunderbolt: 33820
---possible 3HKO on Tauros--- (32590)
Gengar's Psychic: 32040
Chansey's Ice Beam: 29070
Tauros' Blizzard: 28320
Starmie's Thunderbolt: 28120
Snorlax's Blizzard: 27360
Lapras' Thunderbolt: 27360
Golem's Fire Blast: 24960
Tauros' Thunderbolt: 22420
Snorlax's Ice Beam: 21660
Exeggutor's Mega Drain: 20880
Gengar's Mega Drain: 14240