It's hard to compare, as even Deep Zen runs on much more...modest...hardware than the match version of AlphaGo did. It's conceivable that AlphaGo would get clobbered on Zen's hardware, or that Zen would clobber AlphaGo if that team had Google-eseque resources available. But there's no reason to believe we'd ever see such a fair comparison. It makes no sense for either team!

Zen is commercial software sold to people with a normal PC, so obviously reaching AlphaGo performance on AlphaGo hardware does their customers no good either.

It's for sure stronger than Darkforest. Some free PC programs like Leela have reached Darkforest levels on normal PC hardware (Darkforest used 44 NVIDIA Tesla cards, Leela uses a single normal "gaming" GPU), and Zen is several stones stronger than Leela.