I feed Re-leve. I started with the Saracens endurance mix as, like you, I wanted something that would help with stamina, but when I rang their helpline they told me to go for Re-leve as my horse has Cushings and apparently cereal free is better, even though he's never had laminitis. My horse loves it, it is certainly helping with his weight and we are in training for a local race, so he's doing quite a bit of fast work. Prior to Re-leve he dropped weight really easily with an increased workload but he's looking great this time, although he does have two large feeds a day. He's not fizzy at all, in fact sometimes I wish he had a bit more fizz, but he isn't struggling with the work I'm giving him at all.
However, as I know to my cost, all horses are different and what is ok for my boy might send yours into orbit!