Remember that API 5L pipe is specified by minimum yield strength and AWS electrode classifications are by minimum tensile strength. So, do the electrodes achieve minimum yield specs? I guess you could justify it by testing and using the typical 'as-welded' data from the mfg. for additional support. But who's to blame when a batch comes in lower that the 'typical' or who would even know? It's best to match an electrode with minimum yields to the pipe material minimum specified yield. E90 being more common for X70 pipe. What percent SMYS is the system designed for? Would the lower yield electrodes change the class of system or SMYS percentage? The E80's are very close so probably not - but something to consider especially if your running > than 40%.
B31.8 allows qualification by API 1104 or ASME section IX. However, in both codes you qualify by tensile strength. I'm guessing, though I don't really know for sure, that this is because failure is related more to tensiles than yields. Yielding is the point at which materials start to deform plastically. Subsequent to this is a work hardening regime that will actually strengthen the material. It is tensile strength that is related to ultimate failure.
However, you need to determine which code/standard is being used for qualification because the specimens, the locations, AND the dimensions thereof are different.
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