We rebuild the page closest to your sale and run it against the one you have now, on your own live traffic. The scoreboard is revenue per visitor, not a dashboard metric.
Usually the product page, because that is where the sale is decided. One page, rebuilt properly, rather than a list of opinions to argue about.
Old page and new page run at the same time on your own traffic, so seasonality and ad spend hit both equally. The result decides.
Two or three tests a month after the rebuild, each one measured the same way. Fewer opinions, more tested changes.
Every change is judged on revenue per visitor from your own store, not a case study from another brand.