No it won't, the difference between Helvetica and Arial at small sizes is barely noticeable. Furthermore, most Windows users won't have Helvetica anyway, and if they do, it looks totally broken.
The appearance does matter more for display text (logos, headings, etc.), but you're using font-face for those anyway.
The appearance does matter more for display text (logos, headings, etc.), but you're using font-face for those anyway.