Personally, I wouldn't go for a card with a blower-style cooler like that, as those types of coolers tend to run somewhat hot and/or noisy. The only real benefit they have is that they exhaust heat directly out of the case, which can potentially be helpful in some very small cases with limited ventilation.
As for clock speeds, they should be largely ignored when comparing different graphics cards, as other factors, like core counts and the design of the memory system will tend to play a larger role in determining the performance of differet models. You would need to check reviews to get a good idea of how different cards compare. And most designs of a particular card from different manufacturers will tend to perform fairly similar to one another, usually with only a few percent difference separating the fastest factory overclocked models from the stock-clocked models.
As far as how the performance of cards compares in this price range, in general, a 2070 should be around 3-5% faster than a 2060 SUPER, and a 2070 SUPER should be around 10-15% faster than a 2070.
And while you did mention wanting RTX (I assume for the raytraced lighting acceleration in the handful of games that support it so far), it is worth pointing out the Radeon RX 5700 XT offers performance that's roughly in between a 2060 SUPER and a 2070 SUPER on average, which makes it a little faster than a 2070 in most games at prices more similar to those of the 2060 SUPER. It does lack dedicated raytracing hardware though, and most of the models currently available have blower-style reference coolers at the moment, since models with alternate coolers have just started appearing for sale within the last week or so.