The below set of figures refers to the level speeds of the Bf 109 K-4. Little is known about the airframe conditions, date, or wheter the results are based on flight trials or calculations, however it appears to belong to a series of papers which also include performance specifications for the Bf 109 G-6 and G-14. This may point that the they are preliminary figures from around May 1944, before the start of series production.
Performance is given both at 30-min 100% Kampfleistung, and 10-min 110% Sondernotleistungr outputs. The latter would refer to using MW-50 methanol-water boosting along with either B-4 or C-3 fuel grades, for respectively 1,8 or 1,98ata boost, 1850 and 2000 PS output at SL.
In comparison with the more detailed Messerschmitt AG calculted dataset, dated January 1945, the below graph shows about 10-20 km/h slower level speeds at idential engine outputs - these may be explained with the airframe conditions not complying to the 109K airframe standard (fully retractable and fully covered tailwheel and main wheel), and referring to an airframe with non-retractable tailwheel and the lack the wheel well cover doors. See here for the level of extra drag caused by these items. However, without the knowledge of this paper`s detailed, such are merely educated guesses.
The graph also show significantly (ca. 1000m) lower rated altitutudes. This latter characteristic is strange as the level speed graphed below show the total absence of rammed power gains at critical altitude, ie. at 1,98ata, compared to static (unrammed) rated altitude of 5,1 km (note : later DB 605DC manuals give this as 4,9 km), the level speed (rammed) rated altitude is also the same 5,1 km, compared to the realistically expected (and shown in other datasets) 6 km (rammed) rated altitude.
If you have more information on these papers, please e-mail me.