How do I know when my frame is too small?

When it's too big, it's obvious. If it's too big, I can't stand over the top tube and I can't lower the seat enough to reach the pedals comfortably. But what if it's too small? What problems are there which can't be rectified by a longer seatpost, increased setback and a longer stem?

The reason why I'm asking is that I can get a good deal on a used road bike frame. Right now my seat tube 47 cm is C-C, top tube is 51.5 cm C-C, wheelbase is 102 cm. I'm 5'6" with 29" inseam. The frame I'm looking at will be smaller, I don't have the exact measurements yet but it's 650c and most likely I'm looking at a 49 cm top tube and 92-93 cm wheelbase.

I'm wondering if I can adjust it to fit me, and if I'm going to run into any problems because of the shorter wheelbase.