Both are good. ISO is not necessary but it does act as a layer of insulation to stop heat from being conducted from the engine block into the runners and plenum. How much good does it do? I can't really say.
If you like the sound and look of the exhaust, get it. Those are the most important factors. Unless you plan to go FI in the future. Then you might wanna look into 3" systems.
I had BONOSS wheel spacers 20mm on my car for almost 21,000 miles, with no issues whatsoever.
Maybe you can try what I installed.
They can customize the thickness and data that I want, so that I can install new tires with different data, and the customization time is very fast, just 1~3 days.
They have aluminum alloy 7075-T6 and 6061-T6 options. 7075-T6 will be more expensive but better in quality. In fact, 6065-T6 is good enough. Its tensile strength, yield strength and elongation can support our normal use. And its lugs are grade T10, studs are forged grade 12.9.
A forum community dedicated to Nissan 350Z / 370Z and Infiniti G35 / G37 owners and enthusiasts. Come join the discussion about performance, modifications, troubleshooting, exhaust, turbos, maintenance, and more!