Tire ratings relative to each other. If you update to tires that have a 4500 lb capacity, and currently have 3670 lb capacity, you've increased your buffer. Do you need it? You have to answer that question. Blowouts aren't fun and can cause thousands of damage even if you or others aren't hurt.
When I drove my SRW with my current TC, I went for 19.5 Gs because I liked having the extra margin of safety. Probably was overkill, but that's ok with me. I couldn't get by with a DRW at the time since the SRW was my daily driver and even it just barely fit where I needed to park at work.