That's an interesting comparison, but a single time extrapolated from a lap around a different layout doesn't work.
It does. The track the Zonda R posted a time at and the track Estre circled in 2014 is exactly the same track (unlike the 2018 laps, which occurred after substantial re-surfacing and smoothing of bumps in 2016 and 2017). There's also many more other laps that similar times can be derived from (from VLN events). It's well known in motorsport circles that GT3 cars are close to 6:30 times around the Nordscheliefe, that's not really up for debate.
If you want to shift the comparison to the fastest GT3 race times, add 10 seconds to each lap, which are still many seconds quicker than the Zonda's time. But then you're comparing times on either high fuel or on worn tires to the Zonda's clear track time attack, so that's not completely fair either.
It's also just a single track.
It's the only track where a direct comparison can be made.
If we want to make an assumption based on a single lap around a more balanced track than the Nordschliefe (which as great as it is, it isn't a balanced track at all) the Zonda R did a lap at Top Gears Dunsfold test track and set a time of 1,08.5 which was slightly faster than the Aston Martin DBR9 which set a 1,08.6, the Aston however being a GT1 spec car.
Interestingly, if we compare the DBR9's times with GT3 times on tracks that have not changed in layout since 2005, GT3 cars have marginally eclipsed the DBR9 on several circuits (Nurburgring GP-strecke, Donington, Hungaroring), though not quite at power tracks like Monza where the DBR9 retains an advantage.
I do know the Zonda has narrower tyres than the Vantage GT3, and the tyres it runs with are Pirelli P Zero's, that could prove the difference on some tracks. Bear in mind though in a race with qualifying, the car would be wearing tyres appropriate to the situation.
also zonda r used its standart compounds.
As far as I can find, the Zonda R uses 325 rears (like a typical GT3 car), though with narrower fronts, and
the tires used on the nurb record run were slicks. More than just a single tire construction, P Zero is a term used to tie-in Pirelli's performance tire range (you can see the branding on even their F1 tires), and I can't find any evidence that the Zonda R set any of its "record" laps on street P Zero tires.
As far as tire advantage, I have no idea how the Zonda R's special slicks compare to 2014 VLN/Nurb24 slicks, so I won't speculate on it.
Regardless, I'm quite confident that the Zonda R isn't a step up in performance on GT3 cars, if it is quicker at all.