I tried Elemental Force on the Headless Horseman and it was just 1% of my damage. HH is a short fight with just a single target for most of it, but with a short period with adds, so it's not a bad benchmark. I'll probably look at Windsong effectiveness on the same fight today.
Edit: Forgot to mention that if you look at World of Logs, the raid overview page shows Water Elemental damage, but the player page doesn't include pets, so the damage percentage for Elemental Force appears slightly inflated because of that. Pet damage will probably scale with Windsong, but not with Elemental Force. Minor thing, but it affects the numbers a bit for frost.
BTW, it's a bit unfortunate that the caster weapons are now 1-hand. I have two Klaxxi sabers and wanted one of them to be a "blue lightsabre" Spellfire Longsword
and the other one "gold" Blade of Wizardry
. Unfortunately you can't transmog 1-hand weapons with main hand templates. :( The best solution would probably be to retroactively convert all caster main hand weapons into 1-hand weapons, as long as the models are OK for offhand animations (melee transmogs using caster weapons).