Good advice from Trevor.
It's expensive and having buyer's remorse after the fact is never fun.
Charlie, if you already have shorty headers and like the sound volume of your current setup, then go ahead and get the cams and leave the exhaust as is.
The shorties will help scavenge gases to help the cams. The cams by themselves will not cause more drone than is already present.
Nor will they increase the sound level. They will add performance and change the song played by the exhaust.
Max, the cams you just put in are good for around 20 rwhp on their own.
The scavenging from LT's will add roughly another 20+. My results were cams 18 and LT's an additional 22 for total of 40, in y 05 automatic.
I don't have numbers on shorties. They will help also, so maybe guess 50% of LT's. That would still help your cams breathe for better performance.
For anyone, if you share your car with your significant other and do trips like this past weekend, consider diligently LT's. They add sound inside the cabin as well as outside. For example, it becomes hard to listen to the radio or have a conversation, and it doesn't go away.
The way I explain it is that to listen to the radio, you have to turn it up so loud that it becomes noise too, instead of music.
So then you have noise from the exhaust and from the radio.
For example, my wife would not have enjoyed this past weekend if we had been in the green car. Maybe she would not have come.
One way to control noise level is to retain catalytic converters and use conservative mufflers (or axle backs).
Something like a street or touring muffler. But adding a low noise muffler is kind of counter to what the LT's are all about, which is high flow.
One might as well do shorty headers and control the final noise level with the muffler...
High flow cats on the other hand, with LT and mid pipe combos, compared to no cats is only a 1 to 3 hp difference, which is negligible.
Especially in NB where cats are part of annual inspection.
Hope this helps. Don't hesitate if any questions. I speak from first hand experience.