The R500 is a traditional design, not a compact frame , so 5" of exposed seatpost would give a frame with adequate standover height.
The 10" of exposed post would be appropriate for a compact design, which differs in the that top tube instead of being horizontal, is tilted down to meet the seat tube lower, hence more seatpost is needed. You shouldnt size a compact frame according to traditional methods (ie by standover clearance).

With your R500, the major difference between the 53cm and 52cm is the length of the bike. The smaller bike is 0.5cm shorter.
How does the bike feel for length. Do your bars come easily to hand without feeling distant or remote? Can you use the drops, holding them by the hook of the curve rather than holding near the bar ends.

If you are chosing between 2 bike sizez, the smaller one will permit you to move the bars lower, and the larger one will have the bars higher. It depends what style of riding you do, but most riders tend to have their bars too low for the riding they do.