I rather had the opinion that the 109 pilots in the Battle of Britain were rather experienced, ore atleast more experienced than their opponents from the RAF anyway.
Anyway, the slats were a nice reminder that the aircraft was close to stalling. While it was a good thing that they "took over", one would still know that there was not so much a space any more for error, and unlike the Spitfire, the 109 could be forced into a nasty snap, slats or no slats.
But generally putting it,,,,giving the same amount of thrust to each of the opponents, the Spitfire would definately be the winner of the turnfight, maybe even also climb and run;)