When it comes to recoil springs the 16.5 will work fine with 45 loads, including the +P loads.
I ran a 16.5 recoil spring when I was shooting my heavy pin loads that were making a 218.5 power factor, my pin loads were like a +P+ load.
If a 1911 is ejecting brass to far there's better ways to solve the problem then over springing the gun with a heavy recoil spring.
Now as for the issue with the Gold Cup, the stock ejector should work just fine with a polished & tuned extractor. I would start with 24 ounces of tension on the extractor, add more if needed.
Regards
Bob Hunter
www.huntercustoms.com