The lower the string count and thinner the string ,you get less inertia. Which makes the limbs a tad more violent. If you have tip that can handle the extra speed, you are ok. If the bow does not have limb tips of the synthetic, bone, antler, etc. etc, nature,you can crack your tips. I have seen several bows that had the tips split and crack because they did not have the right kind of tips to handle a fast string. I have had no problem with fat dacron strings before, so I see no need to change. I do have a fastflight string on a recurve I built. I do not see enought difference in speed to justify a possible tip fracture.

Something else to consider. I have made bows for people that want fast endless loop strings. I build what they want. But do to the extra speed, I need to add a more hindering string silencer. When shooting the bow in, and after getting it set for hunting, I have noticed the added speed due to the skinny string is negated by the denser string silencers.

Just some of my observations.