Like everything on these builds, just depends on what you want. For street driving, the HP difference (if there is any) shouldn't be high on the list of importance IMO. I doubt you wouldn't notice any difference. Temperature also is maybe not a decision point. I agree the SS pipes seem to cool off a little more quickly. But absolute temp once you stop and are climbing out won't be all that different. Either are going to hurt you. The Boig pipes are a bit quieter. But the Gas-N's aren't bad. Also depends a lot of what engine you're planning. Not every engine setup sounds the same. Some are harsher (or not) than others. Regardless of what pipes you choose, I personally strongly recommend ear plugs of some type all the time. Not just because of the side pipes, but wind noise, traffic, etc. all combine to make a very loud and damaging environment. Don't underestimate that for yourself and your passengers. Appearance again depends on what you want. The Gas-N's are stunning. But not everyone wants the high polished shiny look. I personally would avoid J-pipes. Everyone I know that has them has problems with them. Stick with 4-into-4 headers. Again IMO. Finally, not sure your price is comparable. The Boig price includes headers, right? He typically sells them as a package. Gas-N sells headers too, but that price is only for side pipes.

Full disclosure, I'm a huge Gas-N fan and user. Four builds, all Gas-N. You can see them on my 20th Anniversary Roadster in this video produced a year or so for our local club. Also enough drive-bys you can hear what they sound like. In this case with a Coyote and straight tube 4-into-4 headers. https://youtu.be/gCBLH-mr7ME