I am curious as to how important ventilation is when it comes to aluminum free float tubes.  I am thinking mid length or rifle length gas system here as I'm sure it makes no difference on a carbine due to the shorter handguards.  Also I am aware that HBAR's would be less affected.  I was wondering if some of the tube designs would hinder accuracy during a longer shooting session due to the barrel overheating because of the lack of vents cut into the tube.  Is the wider opening near the gas block sufficient for ventilation or should I look for one with vents in it?