The answer to your last question is something i can't answer myself since i never found a full estimate. For now I'm just going to have to hope for a good BP zapdos this run. Good luck with your run dude!
Yes they do though i can't confirm much speed boost i found.The problem is i abandoned boost testing for many reasons one: i thought boost pertain to what location your at in the game turns out i was wrong since citadark has pokemon with insane rises and drops of speed boost. Two: sadly it can only be done with speed and is too time consuming.