I have just put the o-rings on my heavy caps on my Carol Brass 5000 YLS. After about 15-20 minutes of testing diferent o-rings tickness, tweeks and alternations between standard caps and heavy caps, I can say that I feel preety big diference in response and intonation in a better way. High notes are even clear now. I am very happyy about this.
It isn't a very big diference but is noticeble enough.