Exponential... I have been shooting Viper HS-T (same glass as PST Gen1) 6-24x50 VMR-1 scopes for over 10 years... They're now extremely outdated. The new Viper HD is leaps and bounds over the PST Gen1 glass... And the turrets are not even in the same league. The new Viper HD turrets are a massive (and MUCH needed) upgrade over prior generation Vipers.
To put this in plain terms, IF (hypothetically and anecdotally) you say the PST Gen1 is = to a Tasco World Class, then the new Viper HD is = to a Nightforce ATACR. The difference is that vast. They're not even in the same ballpark.