You usually can't tell a whole lot in advance, only enough to narrow your list by excluding products which fall outside your specs or budget.
Reference cards are built to reference spec, of course, while factory-overclocked cards will have higher clocks than reference, of course. But no real way to tell beforehand how much higher they can go.
Good reviews will give you an idea of what to expect, especially if many reviews compare many cards. The best reviews will provide some takeapart/analysis to show you what sort of hardware is involved. The card maker rarely modifies the core basics - GPU ASIC and VRAM, etc - but often improves the VRMs and cooling hardware so that the core parts can reliably be pushed harder and faster. Nonreference ASUS cards tend to have quite robust power and cooling hardwares, STRIX and MATRIX/POSEIDON/etc cards tend to consistently do well on overclocking.
My personal experience - which is not truly extensive - is that when a manufacturer offers different tiers of the same product then you'll almost never be able to push a lower-rated and cheaper version to the specs offered by the next-higher-rated and more costly one, the manufacturer binned parts and of course doesn't use the best ones on products which sell at lower costs. Yes, an argument can be made that sometimes manufacturers will deliberately low-bin the better stuff to fill demand on the faster-selling stuff ... but don't count on it and don't be disappointed if you lose a gamble based on this hope/expectation, some people always win this game (and some try to play the multiple-RMA-reroll game until they get better results) but the vast majority only get exactly what they paid for. The corollary is that when you buy a card from a manufacturer which doesn't pre-bin for multiple card models then your chances of lucking out on epic parts are (theoretically) better.
Silicon yields - so-called "ASIC qualities" - also improve over time. Later-run parts tend to have better overclocking thresholds and power efficiencies than early-run parts. Later-run parts also tend to have more reviews and "under the hood" information available online. There's just no real way to know how well first-wave cards are going to overclock in advance. The premium on factory overclocks is highest on the very earliest products and on the very best of the best of the latest products within any card family - you could pay +100% price for +15% performance, it would be smarter to SLI/CF a second card!
"All opinions are not equal. Some are a very great deal more robust, sophisticated and well supported in logic and argument than others." - Douglas Adams
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