The only way maximum speed could be increased is if the pilot manually reroutes power from other sub-systems to the engines (the complete opposite of what Dutch, Tiree & Pops did at the Battle of Yavin; big mistake). I don't recall if this ability is limited only to craft designed to carry astro droids, though. Hmmm...

It has been suggested that engaging deflector shield systems creates an invisible aero-dynamic form for craft performing in atmospheric conditions, but I haven't seen anything that indicates this statement is canon.

Personally, I'd much rather have manual control over the S-foils. I don't like it when they open and close based on my acceleration. ME LIKE FULL CONTROL!

Everyone thinks that the wings closing is equal to more speed, but in the movies you hear them say to open the s-foils and accelerate to attack speed.
The s-foils closing to gain more speed was a gameplay tactic used by the Rogue Squadron games, which has no real basis in actual lore.

But at the other hand, during atmosphere flight, u gain faster speeds when wings are closed, due less wind the wings take this way, cause with open wings at high speed in atmosphere, the wind can curl between the wings and make the plane very unstable

For space combat, this isn't a real problem, u have more space to strike and there is no fraction, hyperspace is another story, another space, so I think more atmosphere like conditions in this other dimension

Can't really tell when a TIE is slowing down unless your close enough to hear the engines.

Doesn't matter to me either way, but in regards to balance I'd leave them open all the time.