Originally Posted by FBinNY

William,

Heavy rider almost always do better with more width rather than more pressure. Unfortunately the selection of tires for 27" i more limited than for 700c, but seek out the widest tires you can find.

For comparison look at the auto/truck world where heavier vehicles use bigger (fatter) tires. The pressure doesn't change so much, it's the size that does. Here's a guide to optimizing pressure and width for various weights. You'll see that you always have a choice between narrower/higher pressure or wider/lower pressure, but overall you'll do best wider rather than more pressure.