There is a point of diminishing returns ... 20% tint is nearly twice as dark as 35% and only blocks out 10% more heat. They both should block 99% of the UV.
Thanks everybody. I've used 5% for years, so I'm used to the darkness. However, I agree that it can be too dark at night. I really went with 5% on this to protect the interior and also look good. I don't really drive this car that much and rarely at night.