I have the Springfield Super Match with the Fiberglass McMillan Stock and it is way heavier than wood!!! It shoots better than I do and I have embarrassed plenty of weekend warriors with their bolt guns!
91Bravo is right on! 10 years ago the Fiberglass was the way to go. Varying temps, humidity, etc did not effect the weapon as much as it did with a wood stock.
However unless you are looking for turning it into the absolute best tack driver a semi-auto can be, then get the composites as they are really amazing!
I assume since your looking at the Scout your not looking to make it the Ultimate Reach Out and Touch someone Semi-Auto. So go composite.