BUY the CZ 97 if it's that hard to come by. DO NOT trade the 220 ST for it, as the 220 ST is, in my opinion, a very high quality weapon.
220 ST's got a slimmer grip, better trigger, better sights, better ergos (for most). It's just a more refined weapon. Mine's SUPER accurate. You need to shoot yours more.
97's got higher capacity. Haven't shot one yet, but from all accounts, a very rugged, reliable, and accurate weapon also.
I traded away a 226 ST + $$$ for a Les Baer Supertac w/ 1.5" guarantee. That's trading UP, not DOWN. Trading the 220 ST for a 97 would be trading down.
Just buy the darn thing.
Edited to add: Ah, I see the 97 is no longer on your wish list, but the 220 ST is still in your dog house. Why? If you're looking at an HK USP .45 and a CZ 97b, you must have pretty large hands. Keep the Sig, it's one of those guns you'll regret getting rid of later on....