EIA and Blotting grades of secondary antibodies are purposefully made for a particular assay (EIA) or WB to optimize its specific binding and detection through conjugated HRP. Although targets are same for both antibodies but defining its volume and concentration from one assay (EIA) to another (WB) would be tough and in that way you may not be sure of chemiluminescence detection of appeared band on the PVDF membrane. Even if you successfully complete WB with EIA grade antibody, you may not be in position to convince yourself on the authenticity of data generated. This will result the loss of your important sample time and energy.

If your purpose is to just see the presence or absence of your target protein then you may try it out, but may not be appropriate for quantitative analysis (densitometry of bands on PVDF). Its up to you...

I'd expect that the EIA grade has a higher or more defined HRP activity than the WB grade. Possibly both ABs you are mentioning are from the same labeling process, and just differently graded batches by quality control after the HRP conjugation.

For ELISA, substrate conversion should be performed in about 15minutes, in WB you can play around (and probably will do it anyway) with exposure time.

You should be able to find some information on HRP activity in the data sheets, stated as a RZ value (Reinheitszahl) or absorbance ratio.