If I understand it correctly, it should not have a big impact on overclocking. Multiple Vid just gives yield improvements in some cases. It is multiple in the sense that a batch of chips may use different voltages, but an individual chip still has a fixed voltage.
It is unlikely there will be much of an increase in voltage due to multiple Vids. Maybe some 1.55 V chips will appear (maybe not). But some chips will definitely get a voltage decrease (maybe 1.475 or 1.45).
If you're overclocking, you want to find the magic chips with the lowest Vid. But of course the only way to know is to open the box and see if you got lucky.