The ZF is his latest model which started appearing earlier in the year, the ZE is the original model which has been around a few seasons now. The ZF is a fairly different outline, and I believe a different construction method. Arguably you would say any 'newer' model is better than the older model?
I haven't really sailed either to tell you what's best, but I see TONS of both Z models on the tour these days, which suggest they are more popular than Virus or other fins. At the front end of the fleet there is more guys on ZF fins (ZF 71 S- on 167w and ZF 70 S- on 167normal).
Low wind limit will probably depend on what board you are on. I would think at your weight on a 167w you could get going in anything above 8 knots with a 68 and 11.0m. The wide board does not need much power from the fin or a big sail to get moving... I only use 11.5m as my lightwind sail and I'm 85kg.
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