Hi,

well we were talking about <small> originally. <small> has no semantic meaning, as little as <span>, so you might as well use it. If it was deprecated, I wouldn't, since I prefer my projects to validate as strict.
The point of interest is always: Is there a semantic tag that makes sense? You mentioned <strike>. That's deprecated since it has no semantics. <small> hasn't either, don't ask why it's not deprecated, no idea.
In the case of <strike> you might use <del> instead, if it makes sense. By default in common browsers¹, it's displayed the same way, but it has a semantic meaning: This part of text has been deleted.
However, I don't know a proper semantic element where Alex used <span class="small">, so <small> would do nicely.

Arnd

¹) However, I would add del {text-decoration:line-through;} in my stylesheet to be sure.