I have an old LRP Speedo with a nosram 7.5 in my spares as an emergency/wet conditions backup. You are welcome to try it for a race meeting to see if 7.5 is enough before you spend your cash. It's not the latest stuff and i haven't used it for ages so if it sets fire to you car i can't take the blame
Anyway if you want to try it, just let me know and i'll bring it with me next time.