Define 'optimal' and 'business PC'. Do you mean an email/word processing machine, something to do web design, a 3D graphics workstation, a server (and then we'd have to get into what *kind* of server), or something else?
Are you looking for 'the cheapest thing that will work', 'best bang/buck', or 'cheapest with super-high performance', or something else?
In short, your question is *incredibly* vague.