Re: Really need advice on reel size...
"Is over sizing a 9-wt rod with a 10-wt reel a terrible idea?"
Not in the least. With the exception (just my opin) of very light rods 'bigger is better' as the reel is a counter balance for everything beyond your hand on the cork.
Reel weight choice frequently comes down to do you want to fish tip light or tip heavy.
"We sleep soundly in our beds because rough men stand ready in the night to visit violence on those who would do us harm." – Winston Churchill