I just got a 55w SOX, found a extreme amount of black coating on the ends, and also found out that it only draws 52-54 watts and even later dropped to 49 watts from a WH3 with both outputs tied together. Is that underdrived, and is the lamp bad or really good (with the black coating)? I also heard that the black coating around the electrode area is actually the IR reflecting coating. Also, do I need a bigger ballast for this lamp?

To determine, if the lamp is bad or good in terms of the real power draw, you would have to use the officially rated ballast, measure the arc voltage and compare the measurement with the lamp rating.
In your case most likely the ballast deliver less current than this lamp need for the rated power.
Did you at least check another (known good) lamp on the same ballast?

But good vs bad lamp lies mainly in the light output and starting reliability.

The dark rings around cathodes in the arctube have nothing common with the IR coating (IR coating is on the outer). They are present on many new lamps, so it is not as clear, whether they are a real signature of lamp wear.