Ok....
So here is the deal.....
1)Most of the time, a 109 can LOOSE its energy faster than a spit, which means you can get to corner faster.
2) Once there strive for the snap shot. Also, a spit only has 1 notch of flaps, full or none, which means in a 109, drop one notch, at almost 200, force the spit to drop flaps (all flaps as he only has one notch), then climb out or enter a steep vert rolling scissors eeking out every drop of e you have. The act of forcing him to drop full flaps, will burn his e much faster than you, giving you a noticeable speed difference. Oh and look, a k4 can get back to corner very fast from 195 to 230 in no time, where the spit has prob will have to go from 150 - 230ish. Now, some of the best pilots will just lag turn in the spit, but most will pull as hard as they can with everything they got as they put faith in relying on their turn abilities.
3) If fight gets slow and your not on top, dive out and repeat.
4) Lastly, spits dive better than k4s, so get into a nose down vert scissors, (drop full flaps, cut throttle), chances are, the spit will not do everything and overshoot as he accelerates better and retains e better nose down. (Poor e retention is a double edged sword).
Next time in the ma, do this... as a test... (this is not a good strategy as a acm but it proves my point)
1) Get a spit on your 6 and dive with him following... ( make sure he is close, within ~400, so once you see him drop your nose down steeply, full wep, etc)
2) Once at 300 ( hopfully before he shots you), level out and cut throttle, and do as hard as you can, turn to the left. Also, make sure to throw some rudder in there to keep the 'ball' in the center.
3) watch him overshoot as he trys to follow you in the turn.
Why this works: 109 retains e much worse than a spit, so get to corner faster and your turn is tighter.
A Spit at 300mph isn't going to stay at 3 Gs in a turn fight with a K4 when it can increase it's turn rate and decrease it's radius by pulling harder and slowing down.
And when he blows his 'e' to pull for lead, go for 'e' and climb!... you have the same climb rate as him (if not a tad better) and from the spits perspective, you will disappear! (as he has pulled lead for the shot, so you under his nose, in which case you roll and pull up, and he wont see you do it)
I'm sure FLS can elaborate more on this.