Someone out wheel shopping asks us this question every day. Actually, they usually ask, "Which should I get - RFSC 38s or RFSC 58s?" To which we usually reply, "You know, we also offer RFSC 50s via pre-order, and will begin stocking them in June," hoping to simplify the decision by splitting the difference. Instead, it complicates it.
The answer, of course, is to get the RFSC 38s. They're 1370g for the set, making them our lightest clinchers - ideal for hilly races or crits with a short sharp hill every lap. The low weight comes from the rims, which are only 390g. So not only are you carrying less weight, you're carrying less rotating weight. The 38s accelerate whiplash fast, making them the perfect choice for technical crits where you need to jam out of each corner, or a race where the finish is 200m from the line and the winner is not the one who can go from 32mph to 40mph, but the one who can come out of the corner at 26mph and be the first one up to 34mph. So absolutely get the 38s.
Unless you spend a lot of time with your nose in the wind. If that's your style, definitely go with the RFSC 58s. At 460g, the rims build into a wheelset at about 1525g. They don't spin up as fast as the 38s, but the added depth helps you keep the speed you've generated, making your long attacks more formidable and your rest time rotating through the paceline in the break more fruitful. Oh and for a long sprint that's all about high speed, you'll adore the 58s. Aerodynamic benefit is more evident at high speed so you'll save more watts at 36mph than you will at 32mph. So don't even think about it anymore - get the 58s, for sure.
Except if you like climbing, and crits, and attacking, and sprinting, and accelerating, and conserving energy. Then the 50s are for you. A wheelset weighs in at 1485g, thanks to the 440g rims (about the same weight as Mavic Open Pros). They're not as snappy as the 38s but they're plenty quick. Nor are they as slippery as the 58s, though they have ample speed. They're not as versatile on windy days as the 38s, but are more sprightly on climbs than 58s. So if you do everything - or nothing - well, there is no choice for you except the 50s.
So I guess the answer comes down to who is asking the question, and what qualities of your riding you are trying to either accentuate or mitigate. Ultimately though, they all do everything pretty well so it's not like you're doomed on a solo attack if you ride the 38s, or have no chance on an uphill finish on the 58s. There is no wrong answer. And since every event has a mix of terrain and efforts, I'm not sure there is one that is more right than another either.
So don't over think it and just get whichever you think looks coolest on your bike.