Do we know if the E-4 modelled in game has got (or is supposed to have) a DB 601 Aa engine?
The 'French test' is very interesting, but as Crumpp says, somewhat difficult to use for modelling a E-3 for the sim. The instruments are not the biggest problem really - we can still convert it back, we can also convert the whole test to 'standard day'. The issue seems to be the shape of the plane and components replaced / used, oil, glycol etc... The French apparently had a German manual to compare the outcomes with, and although the top speed was matching, there were some problems with overheating and even engine malfunction (not specified though) resulting poor climb rates when compared to the manual. It took them almost 2 minutes longer to climb to 6000m, that's a massive difference. The 50km/h difference Kwiatek pointed out might also have something to do with the overheating problems - rads were really draggy, but the 50km/h difference between fully open and fully close is rather surprising. Mind you that the difference with and without 500kg bomb was exactly the same at comparable power for a E-4/B (E-3/B), see
here
Regarding the differnce between 'guaranteed' and real perofmance:
I know that's the V15a, but you get the idea why I think it would be generally unwise to modell the E-4 for CLoD after manufacturer's promises.