range difference between r-13m(1) and r-60(m) is negligible, but 13 can get tone at a slightly longer distance. the only reason i would ever bring a 13 is for the warhead size against an a-10 for example, or maybe go for a slightly longer heater-bait. the worse seeker width and turning performance also turns me off to the 13 as well. haven't tested much on flare resistance.
also utilizing your locked beam as a makeshift boresight mode makes r3r shots during vertical bfm really deadly, especially after a few circles if you can catch them near the top of the loop where they cant jink or out-turn the r3r. feels great to merk someone who dumped flares when you launched B).
my general loadout is 60m x 4 and r3r x 2 99% of the time for cap as well.