When I first went to 35s (from 32s) I was a bit surprised at the slower braking. After doing some research on EBC Yellows at the time, I ran across a thread about Black Magic brakes that Blaine sells. So I tried them. Never had to break-in pads before but did so and the difference was pretty significant. That was in 2012. Bought a new JKUR a few months ago and it actually took longer to stop than my JK with 35s. Not bad but it was enough to where I just bought the front Black Magic pads this time. The difference, again, is significant. I have heard of EBC's new Extra Duty pads and have talked to the Tech there. They sounds really good too but are still a few weeks out. I could not wait. Either one will be much better than stock but all this said, I am not sure you must have them with 33s. I would change it given what I have experienced. The bite is a lot harder and stopping distances shorter. When I turned my last JKR back to stock, I left the pads on. When I traded it in, the GM ended up driving it too. When he got back, he came to ask me what I had done to the brakes. He did not see bigger rotors so he was curious because it braked a lot better than the stock Wranglers. Just changing the front pads (if your rotors are still good) will cost you ~$125. If you need rotors, look for Centric rotors. If you do upgrade, post back with your impressions.
"Downside" to better braking- increased brake dust. It does not bother me but apparently, it does bother some people. Just making sure you know this.