Eight pounds doesn't seem like all that much to me, but I'm not a vet. It depends a lot on overall size. We had one cat who was lean and healthy at a whopping 16 pounds (!!!) at the same time as our smallest weighed 7 pounds. Both cats got the stamp of approval from our vet and were pronounced in the peak of health at those weights; one was just a big guy, the other a wee little girl.
One was from Brobdingnag and the other from Lilliput, I guess.
Avery doesn't look fat in his pictures. Has he been to a vet to check out his overall health lately? Your vet would probably say something if he was developing a little too much chunk. This
diagram might also help.
If he is getting a little chubby, more exercise is probably easier to manage (for you and for him, as he won't beg and cry for food with more play-time) than cutting his diet away. Cats love more play time a lot more than they love less meal time.