General advice...Longer is better provided you have the room to use it effectively. Meaning if you can use a 9' rod without banging it off overhanging brush constantly, there are mechanical casting, mending, and reach advantages to having a longer rod, even on small streams.
That said, most of the time, most small stream anglers (myself included) generally fish with a rod shorter than 9'. This is because there are shortcomings that come with longer rods on small streams too...They're harder to hike through brush with, you often don't have room in the canopy to properly cast them, and they're harder to get into the places you need to manufacture the "trick shot" casts that are often required on small streams.
There are guys who like rods as short as 6'0 for small streams, and others who fish small streams exclusively with 9'0 rods. Heck, I've seen some YT vids of guys successfully small stream fishing with their 10'+ Euro nymph rods. All comes down to preference at some point, and understanding there are pros and cons to longer vs. shorter on both sides of the argument. For me, a 7'6-ish rod is about the best compromise of those pros and cons, and what I use most frequently on small streams.
To the OP: Back to the good, general, middle of the road advice...Before you buy, try your 9'0 out a couple times on small streams. You may end up in the camp that likes the mechanical advantages of the longer rod, and is willing to put up with it being too long for some spots. If you feel like you'd benefit from getting something shorter, then do so...If you get something in the 7'0 - 7'6 3-4wt range to pair with your 9'0 5wt, you're set. You can tackle just about any PA Trout situation with those two rods.