"Well FR drivers are not allowed to touch the default of 5%...
And yes it does make a difference of approx 2000' (if I remember correctly)
Also in EASA country the buffet margin in 1,3 and in the US it is 1,2...
So we are often flying around 3000 ' lower than our US cousins"
Plain-plane you don't remember correctly. It's a few hundred feet you lose at the most, especially since FR load their aircraft with a forward CG anyways.
The gain in manuever margin far outweights the minor loss in altitude capability by leaving the CG at 5%.