Clever solutions were possible on the existing equipment. I believe that it was very possible to push the bf109f4 to 700km/h by redisigning the radiators , fully cover the landing gear , delete the nose mgs and use in wing mgff 20mm guns, and various others small aerodynamic improvements. With little production loss such a fighter would be very competitive for 1943. Or a K4 airframe with drum type nose radiator