52-53cm isn't what I'd call a tall stack height. In some brands, that might be shorter than the smallest frame size. I'd think that you'd also have a seat tube length and/or stand over height in mind. To get a complete picture of fit, you need stack, reach and seat tube angle.
For the most part, comfort is going to come from wide tires run at fairly low pressure, as recommended by the pressure calculator at zipp.com.
I've been looking at frames that can handle wide tires. The smallest size Cervelo has a 524mm stack in the smallest size. I agree that a flipped up stem is an option to avoid a higher priced custom. Plus 6 is about 20mm higher than a minus 6 stem.
https://lynskeyperformance.com/gr300...cable-routing/