I think the growth rate is looking good. I had my issues at the 2.5-3 year mark. I fed about as conservatively as you can feed and wound up with an animal hitting the 9 foot mark at 3 years.
The size wasn't as much an issue as the combative, male attitude I had to deal with. That attitude coupled with the size wound up being a double negative. At 9 feet my guy was pretty thick and very strong.
Not my bag, so off he went after a nasty 3rd bite.
This is about you though, and I must say those are beautiful animals and look to be the perfect sizes. I suspect at the 4 year mark you should see the growth taper to a trickle. Keeping the prey items on the smaller side and spacing out the feeding should keep their sizes in check and their health very good.
I'm glad I checked this thread. Retics are wonderful for the right keeper.
Congrats on your progress.