Larry, in regard to strength and force. Readings given by hoe manufactures are based on the backhoe's pressure relief valve setting. This number is sometimes HIGHER then the tractors hydraulic pump relief valve setting. Consequently, the tractor relief valve will blow off before getting to the hoe's rated pressure. This will cause the hoe strength preformance to fall off accordingly.
I have a JD970 tractor with a hyd pressure setting of 2,250 psi and a Bradco 408 hoe that has a pressure relief setting of, guess what, 2,250 psi also. On this rig it hard to say which relief valve unloads first.
The exception to the above, of course, are backhoe's with their own PTO driven hyd pumps.
cheers,
george