It’s less than you probably think.
The sit and reach test that we all did in school lied to us, or at least deceived us.
It has made most of us think that touching your toes is the standard of flexibility, and it missed a great opportunity to help people understand the role of having hamstring flexibility.
More than the first photo becomes a liability that you need extra strength/stability and coordination to control. Most people should not want more than this.
The role of hamstring flexibility is to allow you to bend from your hips and not your back when you bend over. Having the necessary flexibility does not guarantee that you have the motor program (coordination) to even use your flexibility appropriately.
Keep in mind that hip flexor tightness on the ‘down’ leg can show up as a decrease in raising your leg as well. Tightness can deceive us, and it.
Stretching is pretty useless for most of us when not combined with active positions. This is one of the major benefits of yoga – combining stretching with active positions. You need control of your flexibility, not just flexibility without purpose.
P.S. – A Google search of the Presidential Fitness Test makes it appear that this is still being used as the metric.