Some good points.

Everyone has given great advice, so I won't go into specifics, but I will give a general piece of advice: Don't expect PC's to roll 5-6 in their specialty. They won't if it important, they have resources, they will use them. Fate points and aspects are easy to come by, and being able to fate points in your specialty is generally a given (as in you have aspects that are usable on your sheet, not that you always have fate points). Rolling 10 is relatively easy as long as you are willing to spend resources, expect tens and higher every once in a while when you are planing. Do not require them, but don't let a single ten break the session as they pretty much will happen.

Suddenly I'm reminded of the George Straight song 'Write this Down'.  I can't come up with a good parody at this point, but...

Ooh, better yet, Mother of demons.

Make a note.  Underline it.  Underline it twice.  Better yet, cast it in bronze, chisel it in stone.  Remember this.

Personally, While Supernatural speed is fast, it isn't as fast as 40-50 mph, at least at my table.  If he's that fast at yours, perhaps a contest of Athletics vs Driver would be called for because jumping out, stopping and then trying to keep pace with a speeding car would be tough.

Given that Mythic speed has the ability to keep up with a car at a sprint, it sounds fair that supernatural doesn't get it.

I'm not sure Ambush is a good balancing factor.  Ambushes can kill anyone, pretty much.  In fact wizards, provided they've built a 'block against attacks' enchanted item, are probably best suited to survive an ambush.  They get ambushed, their item gets triggered as a defense.  Meanwhile, their party is all defending at 0.  And, unless, they have toughness, they're not any better equipped than the wizard.

Hrm... never really thought about it, but I typically assumed you'd need to be able to react to use an EI.  You have a point, that some shouldn't need that though.

That said, part of the point of my comment is that Wizards -- more than any other 'class' in the game -- are narratively best attacked from Ambush.  In the books, it's repeatedly pointed out that taking a wizard on face to face is just plain stupid.  You take them out by flanking them, surprising them, and outmaneuvering them.

Time-Traveling British Secret Agent

The group was going to engage in some deliberate time-bending paradox creation (by killing a time traveling enemy a second time, in *his* 'past' their 'future'/'present day').  One of their goals with this was to negate the creation of an all-consuming 'black hole' entity.  So I created a character from 'up' and 'sideways' in time, who traveled 'sidebackways' to stop the entity from being created.

And all this was really just an excuse to create a character based on the Kingsman trailers...  Specifically and most lovingly, the bar fight scene.  https://www.youtube.com/watch?v=tukQDg22o9M  Mechanically, he was a pure mortal who had a number of stunts to do things like use discipline and fight for all three stress tracks, dodging, gunplay, and aiming, and then just poured the rest into having a massive pool of FP to just laugh at bad die rolls.  His trouble was [Of Course I Can Finish The Mission] -- a cross between arrogance and an opportunity for the GM to force him to face any trouble head on.  And of course, [Perfect Poise] plus [Manners Maketh Man] provide a perfect recreation of the character from the scene linked above.

He would, literally, just walk up to an enemy wizard and say, "I'm going to shoot you now.  But to be polite, I'm giving you sixty seconds to make your peace with your gods."  And with his pool of FP he could -- probably -- get away with it.

The philosophy of the elements section from the Paranet Papers is an awesome read up.  Just pure awesome.  Air, according to it, is the element of intellect and control.  So think in terms of precise, narrowly defined bursts of power giving you exactly the desired effect.

Forget that Dresden would build an air block as a burst of gale-force winds.  An air specialist might just call up small gusts of wind that interfere with each opponent in turn.  It's not that he keeps that one spell going (which is mechanically what he does).  He throws dozens of smaller, weaker spells with *just* enough oomph behind them to spoil his opponents aim.  Or on the offensive, to trip them up and knock them down.

Think control, think precise, and think of air effects like lightning, fog, wind.  From there... just define what your goal is (attack, manuever, counterspell) and come up with a narrative that fits.

Ignore the rulebook's guidelines for scaling encounters. In a fight, refresh spent doesn't mean a damn thing compared to relative skill levels.

Don't necessarily ignore it -- just remember that skills are just as important.