I read here on Bikeforums often the advice to move saddle aft to take weight off arms and it makes sense, but in my case, I need a forward saddle position to address a tendency to develop patella-femoral syndrome, the most common knee ailment for cyclists.

I'd suggest moving the handlebar to address arm/hand/wrist soreness before you fool with saddle position.

Your saddle height should be the same distance from the center of your bottom bracket on both bikes and the fore/aft position should be the same too. Drop a plumb bob from the nose of your saddle and measure distance from the plumb line to the center of the bottom bracket.

You ordered an XL size Giant and a week later buy a Medium Can-of-ale. So maybe it's too small? I'm always kicking myself in the butt for buying too small. I do it every time, usually I can make it work. In the case of my Crack'n'fail hybrid, I got a performance fit from a comfort bike by buying a size too small and putting a long seatpost on it, for $300 something brand new (the bottom of their line), not counting the 350mm vintage XT steel seatpost which I already had. It's the third Cannon I've owned, love them!

Look at how you sit with arms slightly bent. Is your back at 45º? That would be good. You're old and lazy, so you might want a little more upright. Two options, raise the bars, shorten the stem or both. That's three actually. Before you change parts though...

Get used to it! Get barends, they put your arms in a more ergonomic position, moves elbows in, aligns bones better. I just tried it sitting at my keyboard, try it. Hold an imaginary flat bar, then turn your hands like you would to hold barends. See how your forearms, elbows and upper arms rotate!? What I learned just now by trying that is the problem I'm having with my wrist might be helped by tilting my barends up a little. Don't stick your barends up into the air though, closer to level is better. My wrist problem is from the keyboard/mouse, not the bike.