G.G Hopp is a genuine historian, used to post on this site.
Everything checks out. The New Me 109K4 had a retractable tail wheel and fully covered wheel covers that significantly reduced drag. The engine was better as well, not just in terms of power (1800hp to 2000) but altitude performance, and likely features such as the streamlined cowling and ERLA hood improved speed in tiny amounts as well.
The thin blade propeller(screw) 9-12199 added about 20km/h (12 mph) at 6000m(20,000ft) over the series production 9-12159 at the expense of some climb capability. The prop was highly optimised for high speed flight, but when climbing the aircraft was not in quite as high a speed flight and it lost some efficiency. The Me 109 almost certainly didnt see combat with this prop;
There was another prop, with swept back scimitar tips that added another 15km/h or so. I believe that was only an estimate.
The allegation probably comes from some upset gamer.