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John Thornett (49)
^ according to The 1014 Rugby he's also had the most carries in the NZ Conference this year (41) which is more-or-less a continuation of what he was doing for Aucks last year.
Also on The 1014 (which I believe is also a podcast) they put up ASav's attack stats for the year & he's second or third in all of them for the NZ Conference. It was also implied that he's probably well ahead for metres gained post-tackle.
And the Blues.
As per the FOX stats, here's a quick snapshot comparing Ioane with each of the other NZ #8's. I've included both Whitelock and Frizell here as Frizell fulfils the actual role of the #8, despite playing on the blindside (and vice versa for Whitelock). They're doing some weird stuff in Dunedin. The stats are a bit different that what were provided on The 1041 (e.g. 35 carries for Ioane here vs 41 for them), but I'd be surprised if the overall patters are that different.
And in terms of relative contributions to their teams:
Currently Frizell is the only one able to compete with Ioane across both carry and tackle contributions, though lags behind in both metrics. Douglas and Whitelock put in a lot of tackles, but don't make that many metres. Given he leads the average carry metres, Savea's middling 5.82% contribution to the Hurricanes carry metres can probably be put down to his only playing two matches so far. Seu is stuck with the Chufs.
EDIT: No stats for metres after contact, though.