Order of extent of overlapping is thw amount of overlapping  orbitals of tow atoms can undergo during formation of a molecule. Bondstrength is maximum in SS overlap bcoz here the orbital is closest to the nucleus and thus are the electrons close to it making is more stable, so thw bond strength follows following order SS→SP→PP
						

							
Strength of bonds depends on its bond length. Smaller the length of bond, higher will be its strength.
First of all let me tell you that all the sigma bonds are more stronger than pi bonds. This is because sigma bonds are formed by head on overlapping of the orbitals which are more effective than the sideway overalapping of orbitals in case of pi bonds.
Sigma bonds are further classified as s-s , s-p & p-p bonds.
s-s bonds are formed by overlapping of two s orbitals.
p-p sigma bond is formed by overlapping of two p orbitals andthe order of bond lengths is s-s 
so, order of bond strengths is s-s > s-p > p-p. I hope it helps you