http://www.spitfireperformance.com/spit9v109g.html
F/Lt. Irving "Hap" Kennedy did a stint with No. 185 flying Spitfire IXs from Malta in June 1943 and wrote:
The real compensation was that I was strapped into a brand new Spitfre IX. The Malta squadrons were being re-equipped with "Nines" after a couple of years, including the blitz year of 1942, during which the Spit V was the defense of the Island. Recently the Luftwaffe had moved their latest Messerschmitt Me 109G into Sicily along with some Focke-Wulf 190 squadrons. These latter were superb aircraft and the old Spit V just couldn't keep up to them. The Spit IX, a heavier brute in the engine but the same airframe with the lovely loose ailerons, an additional 250 h.p., a four-bladed prop, and a supercharger that came in with a tremendous kick at 21,000 feet, once more gave us the advantage of a superior performance. We were full of enthusiasm.
... At 1440 Hours, a red flare went up from the dispersal hut, arching over the strip, and my mechanic jumped to his battery. I pulled on my helmet, fastened the oxygen mask, put on my gloves, turned the oxygen valve on, and primed twice. The engine broke into a roar. The mechanic pulled out the battery cable and gave me a "thumbs up" and I was tearing down the strip with full throttle and 3000 R.P.M. Airbourne, gear up, throttle back a little to let the lads catch up, at 4500 f.p.m. climb.
... I had the throttle open and I rolled over and headed on a course to cut the angle toward the 109s, which had separated a little. I wound on nose-heavy trim so essential to keep the aircraft in a high-speed dive. The Spit responded eagerly as I dove more steeply than the 109s, with Red Two and Three no doubt following, although I could not see them.
The controls got very heavy as the airspeed needle moved far right at 480 mph. (Corrected for altitude, true airspeed approached 600 mph.) I could see that I was gaining on the nearest Me 109. That was something new. We were already half-way to Sicily; that was no problem.
We knew from years of experience, dating back to the boys who had been in the Battle of Britain, that the 109 with its slim thirty-two foot wing was initially faster in a dive than we were. But we accepted that compromise happily in exchange for our broad superior-lift wing with its better climb and turn. One couldn't have it both ways. In any case, I was closing on this Me 109, which I recognised as a G. Perhaps he wasn't using full throttle.
We were down to 5,000 feet and our dive had become quite shallow. I could see the Sicilian coast a few miles ahead. Now I was within range at 300 yards, and I let him have a good squirt. The first strikes were on the port radiator from which white smoke poured, indicating a glycol coolant leak. I knew I had him before the engine broke out in heavy black smoke. (Bf 109 G-4 "Black 14" of 2(H)/14, flown by Leutnant Friedrich Zander, shot down 10 June 1943)
Squadron Leader I.F. Kennedy DFC & Bar, Black Crosses of my Wingtip, (General Store Publishing House, Ontario, 1995), pp.58-61.
//////////
You fly ahead, and your wingman 500m behind of you with same speed/altitude. If you dive first, your wing man could NOT overtake you in a dive because he is same dive acceleration with you. Isn't it? So if your bf109G6as is caught by a spitfire IX with same energy and 400m behind of you, you could dive to escape from spit, in the beginning you could pull away from spit but in the end, the distance between you is roughly same as beginning--400m.
With same energy, if you want to catch/get closer to your opponent who dives ahead of you, your aircraft should has the ability of outdiving him. If you are in a P51, P47 or Tempest, congratulations! You could get closer to his bf109 or fw190 in a high speed dive.