Managed to find someone on another forum who had both 10000sw & 10000sw-pg spools, and they confirmed that the 'Power Gear' version has a significantly thinner spool lip.
Presumably the thicker lip on their casting models does aid casting to some degree, but how much is anyones guess. I know plenty of people use 20000sw spools on their 18000sw's but haven't read anything about it signicantly reducing casting distance. Anyhow it's something to keep in mind if your in the market for spare spools.