Here's something to add for those who didn't realize this. (I just now realized it and feel stupid since i've been playing since nov2014). Skill multiplier damage = +25% total damage on skill 1; thus the speed multiplier is boosted by 1.25, as is the base 265% that's added... so... speed will add 1.25^2*spd; meaning 1.5625*speed; this means if you manage 230 speed, you add 359.375% + (1.25*265%) for a grand total of 690.625% of your attack stat. While this is very close to heavy damage skills who's base damage reflect this, keep in mind that skills like Ethna's capture (750% base multiplier) is multiplied by 1.2 at full skill (900%).
Edit: Also, just realized that, indirectly, for theomars, due to elemental king, you're getting an extra 15% damage boost as well, so speed actually, in cases of non-oblivious state, will result in 1.796875x effectivenes relative to your total speed. This also applies to all other elemental advantage situations for ifrits other than Theomars.
Regarding this post, if I'm mistaken (because I'm not absolutely certain about this, but theorized it while preping for free rune removal, and skill damage potential comparison, then please explain what I'm missing here.
Edit2: After working on a spreadsheet for a couple of hours, I looked around and realized someone has a damage calculator in thier blog. I'm not sure that it highlights that this damage multiplier actually multiplicitly affects the contribution of speed to the skill damage but it does seem like something people often overlook. i.e. Shumar = (1.85*spd+250)*1.3 assuming it's fully skilled, further mutliplying 1.85 to 2.405, thus enhancing speed's contribution to the skill; This would, at higher speed values, more drastically affect the spd buff's contribution to the damage total (1.5*281*1.3 = ~1014%, without adding in the 2.50*1.3 constant (3.25); Whille attack buff, on the other hand, will amplify the entire value by 1.5x(constant+spd*constant) instead of only the speed scaling aspect. Keep in mind, 281 speed is specifically, without a speed buff, that Ambush on both Tarq and Shumar will exceed a multiplier of 1000%