ROW car didn't just have better exhaust, it also had larger fuel-head (more fuel at boost). US cars was obviously upgraded with ROW headers but at some point in time it was run with thermal-reactors. Being a weaker car that had more owners (and some were presumably boost-fiddlers) means that it probably lived a harder life. I would pick unmolested 300hp ROW with one picky owner over a leaky US sunroof model any day of the week. PCA guy probably babied it.
US car was obviously fiddled with and yo'll never know if somebody was tempted to up the boost while it still had thermal reactors (a very bad idea with inferior US CIS fuel head). Frankly, even babied US cars that still had thermal reactors rarely survived past 100-150kmiles w/o at least top-end rebuild.
Sunroof is just a added weight (in my book). Non-sunroof 930's are probably more desirable. Check for synch-ring wear in 3:rd gear on both cars.
ROW: Big fuel head (no leaning), euro exhaust, 300hp out of box, one picky owner = good
US: Thermal rectors (until some point), small fuel head, unknown history (?), fiddled with, raised boost (?), leaky engine, sunroof = bad
Pick the one in best condition. Big intercooler will set you back 700$ or so. Top end rebuild (assuming you don't find cracked piston rings which I'm afraid is distant possibility) will set you back much more.
Thank you for your time,