I'm working on a flying humanoid as a possible character race. This is for a non-magical, science fiction setting, with mutations being the only powers. The beings are genetically modified humans. Their wings are part of their arms, and they fold back behind their arms when they're on the ground. They can use three fingers and a thumb when they're on the ground, but they can't use weapons or tools with their hands while flying.
I'm struggling with the SIZ characteristic, because if we're being even nominally scientifically accurate, these creatures would be extremely lightweight, but would have extremely long arms/wings. So I'm picturing them as about 2 m/7 feet tall with a wingspan of 4 m/14 feet. But they would weigh only about 30 kg/65 pounds. Those numbers may be unrealistic--I'm not an aeronautics engineer. But they're about halfway between a California condor and an average pteranodon.
My first thought was to give them a reduced SIZ characteristic--this would reduce their HP and damage bonus but make them more agile and able to squeeze through small openings. (They're tall, but they're much thinner than normal humans.) Then add a special rule that when their height is being considered, double the size characteristic; when their wingspan is being considered, triple the size characteristic. (Not sure when that would be used--Aura attacks, maybe? I've already established that they can't fly indoors or in thick woods.)
Here is my first stab at characteristics. The SIZ is a compromise between their huge height and minuscule weight, with some consideration toward making them a playable race. POW doesn't have a lot of game effects in this world; it's mostly for luck rolls and resistance against psychic attacks, which are rare.
What do you think? Is this playable? Is it realistic? Would you want to play a flying character with these characteristics?