The thunderslides I have seen are black plastic so you can see the difference as the OEM's are aluminium. The thunderslide gets mixed reviews so research first before you spend $$$. I wouldn't have one myself.
For good info on tuning a stock CV carb google the nightrider site and find the performance section for carb tuning. There is a lot of good info on tuning the HD CV carb.
I had one years ago & thought it improved the response over the stock cv pretty well.
Then I put on an S&S & didn't really notice any difference.
try this... http://www.nightrider.com/biketech/hd_cv_mods.htm