G margins and their representation on the PFD
I am not aware that 0.3 is a limitation, but think of it like this:
0.2g you need to bank the aircraft at least 33 degrees to get the low of high speed buffets, and as you know that the airbus A320 family VLS represent 0.2g.
0.3 you need at least 39.7 almost 40 degrees of bank and the airbus long range VLS is representing 0.3g.
VLS is corrected for Mach effect to maintain either 0.2g or 0.3g buffet margin (aircraft specific), I think it happens at or above 25000ft but not positive about the altitude.
From an operation point of view you might want to have 0.3g margin in turbulence conditions.
TruthHurts