A saddle that's too far forward could cause knee pain. A smaller frame often has a steeper seat tube angle, and since your legs are so long, you'll likely need a fairly large setback. (I have about a 36" inseam, tip of saddle is 9 cm behind BB, which places my knee a few mm behind the pedal spindle.) Check to see if your knee is at least in line with the pedal spindle, if not a bit behind it.