Courtman,
Actually the vTOSS is the speed that allows controllability of the helicopter with regards to yaw control. Very similar to the blue line in your plank things.
The decision to land or fly away after an engine failure, in a helicopter, is refered to as the CDP or critical decision point. If an engine quits before this speed you do not have a choice - you will land. After this speed you may well be able to fly away with one engine out.
The speed that allows you to climb at the best rate is usually faster than your vTOSS. This speed is refered to as vYSE.
To put it in perspective, the CDP for a BK117 is around 40 kts (depending on conditions). The vTOSS is 50 kts and the vYSE is 65 kts. Each aircraft is different but these figures are relative to them all.
Hope this helps.