I haven't used any Thai basil in hoppy beers, but I have made 2 Belgian Thai basil beers over the last year. The first was a clone of the Bruery's Trade Winds Tripel. That recipe called for a 15 minute whirlpool addition at flameout of 8 grams of thai basil flowers and leaves, with 2/3rds of the addition or 6 grams being the flowers. I just brewed a spin off of this beer last weekend with essentially the same ratio, except stepped up for 10 gallons. I called it Thaison and was brewed with several Thai ingredients: Thai basil, lemongrass, kaffir lime leaves, ginger, and corriander. It is still fermenting...
The basil carries thru quite well to the finished product. I don't know if I would use 3-6 ounces since I can taste it pretty well in the Trade Winds Tripel, with essentially a 1/4oz at flameout. That being said I am not fighting against a strong hop backbone. I don't think I would go much over 1 oz. if it were me. Maybe, 2oz.? But, it also depends on which types of hops you are using, as well. I like it in Belgian's or as a stand alone spice in a neutral beer mostly, but I say go for it. You can always add more later, but you can't take it away....
Use the flowers as well from my experience.