Always burn the fuel out of wing tanks before engaging in combat. That is part of why you pull the wings off or cannot pull out of a dive. Also make sure a bit of the bottom tank is burned off. Too much fuel onboard is a big reason it is so unSpit like for many to maneuver with. Think of it as a spit8 airframe with about 300 more pounds hanging off the nose and horrendous torque. It's one of the few planes in the game that I only turn off combat trim in a dive so I can recover using pitch trim. Otherwise, it is all over the place with it's own mind due to that torque if you don't spend the time learning how to fly it.
The 150 Oct 21lb boost version was faster than the K4 at Mil and WEP SL up to max alt except for a band between 15-18k. Climb on WEP, it left the K4 in the dust, SL to Max Alt. But, then Hitech would have to perk it again. And the Spit14 over the continent went to war burning 150oct. It just didn't have much endurance for range.
Our 18lb boost spit14 is a dog until it gets above 20k where it starts to be faster and out climb the K4.
All of this is from the comparison page at:
http://www.spitfireperformance.com/spit14v109.htmlThe gonzo AH comparison page, if you put in the spit8, 14 and K4, is very generous to the spit8 and spit14 performance as a generalization to the K4. The other link shows the 18lb boost spit14 as a dog which is what our spit14 is rated.
Compare the 18lb boost spit14 and K4 here, then go back and look at that compared to the other link:
http://gonzoville.com/ahcharts/index.php