If you're 5'6 with longer legs - estimating comparing you to a friend of mine who's 5'6 with a 33 inch inseam.. I think a 54 would be too big... my friend rides a 52-53... the 53 cms a tad big on him, the 52 cm's just right, a 50 cm is manageable....

Use bikepedia to figure out components... that first bike (the trek), really didn't say what model it was or year. The scattante had campy components which looked pretty good... but you'd either have to buy wheels or ride with his dented ones...

I'm 5'1 and ride a 48 cm frame usually, I can just barely clear a 50 cm frame and ride it, but 48's about perfect.