V6 vs V8

VVT allows for higher compression ratio's to be used in conjunction with EFI and the ability for a feed back system to control spark timing and cam timing you can do wonderful things. Add refinements to EGR (i.e. rebreath, a befit added by VVT), computer flow analysis of combustion dynamics, Port flow, and direct injection.

Advancements in technology make it better but also make it more complicated and more complicated to modify.