The RSD and Performance Machine covers/breathers are made to match the similar RSD or Performance Machine Wheel spokes. They have some that come a lost closer to matching the spokes of the HD wheels than the one in the photo with the straight 5 spoke pattern. I was looking at them in the display @ Biketoberfest, you could come close to matching your OE wheels if you tried.
I always liked this simple five spoke style the best, and wasn't trying to match my wheels. Saw this one for a good deal in the classifieds at hdforums, so I grabbed it.
Performance wise, if it's any better, I can't tell from seat of the pants feel. The stock SERG AC and this one are both high flow, and likely provide the engine with plenty of air, but I'd guess the RSD may flow better as it brings in air through a K&N filter vs paper, plus the outer flat side also lets air in.