ZDDP concentration is the same for both.
According to the Valvoline PI sheets :
Cst 100c : 20.0 ( SYN ) and 21.1 ( Regular )
Cst 40c : 147 ( SYN ) and 193 ( Regular )
Viscosity Index : 154 ( SYN ) 129 ( Regular )
TBN : 8.5 ( SYN ) and 11.8 ( Regular )
Flash point : 230c ( SYN ) and 228c ( Regular )
Pour pint : -36C ( SYN ) and -33C ( Regular )
The synthetic has a lower viscosity at 40c which is to be expected, higher Viscosity index which would also be expected, slightly better flash point, slightly better pour point...
The regular VR1 20W-50 is already good, the synthetic is just a tad better.
Although if you wanted a stout high ZDDP synthetic 50 grade i'd steer more towards M1 15W-50 just because it's much more readily available in the States.