if power is what your looking for there is a version of the w123 with a 3litre 5 cylinder turbo diesel.. its the same engine as the 300d wiith a turbo.. very common on the w126 range but i have seen a few 123's with this engine but were both automatic tho..
p.s. i am looking for a w126 diesel.. prefer the SEL(which is six inches longer than the SE).. if you know of any such car pls pm me,, thanx