I'd argue for the Choice sets to be split and that 252 HP EVs be run on Specs Rotom.
252 SpA Specs / +1 Keldeo Hydro Pump vs 4 HP Rotom-W: 85.1% - 100.4% (almost assured OHKO after rocks)
252 SpA Specs / +1 Keldeo Rain SpA Hydro Pump vs 252 HP Rotom-W: 67.8% - 79.9%
252 SpA Thundurus-T Thunder vs 4 HP Rotom-W: 82.6% - 97.5% (likely OHKO after rocks)
252 SpA Thundurus-T Thunder vs 252 HP Rotom-W: 65.8% - 77.6%
252 SpA LO Tornadus-T Hurricane vs 4 HP Rotom-W: 44.2% - 52.1% (guaranteed 2HKO after rocks)
252 SpA LO Tornadus-T Hurricane vs 252 HP Rotom-W: 35.2% - 41.4%
252 SpA Specs Tornadus-T Hurricane vs 4 HP Rotom-W: 50.8% - 59.9% (guaranteed 2HKO)
252 SpA Specs Tornadus-T Hurricane vs 252 HP Rotom-W: 40.5% - 47.7% (roughly a 50% chance to avoid a 2HKO after rocks)
The Speed isn't doing all too much for Rotom-W since it should be running Modest anyway, and it doesn't lose out on anything important afaik (feel free to correct me if I'm wrong), so judging by these calcs I'd say a bulkier Specs Tom is much more preferable.
EDIT: After discussing with QC, due to things like Jolly Breloom, etc., 252 HP is probably better as an AC mention.