It doesnt matter if you have
for(int i = 0; 0<32; i++)
or
for(int i = 0; 0<64; i++)
if you do the right checks in your loop like
if (!entity->isPlayer())
continue;
if (!entity->isAlive())
continue;
it will not make ANY performance differences
Externals are a bit slower compared to internals ( which can make your glow flicker)
But if its coded properly, it shouldn't flicker(my external didnt flicker)
Show some code so we can help