V2 is the greater of 1.1 VMCA or 1.2 VS.
JAR 25/CS 25 states words to the effect of "Close to but not below V2" for certification. I take that to mean that if you fly just 1 knot below V2 due to turbulence or a small handling error then you are outside the certified envelope of the aircraft. If it is a VMCA limit then it can be very difficult to handle.
The UK CAA tolerance limit for an EFATO in an LPC is V2-0/+10 knots.
So for all these reasons V2+5 is the ideal place to be!