I'm not sure who on here has a financial incentive on recommending supplements, but.....
A bull ration is not what you want to feed a steer - at any point in his life. For good reason, they are the opposite of what you want to use.
We feed a lot of show steers and have for a long time. I don't necessarily disagree with XBAR, but I can't get most of ours (especially black calves who are at a similar stage to yours) to eat a true finishing ration in the summer without having issues - diarhea, low intake, etc. I just tried to push two onto one and had to back off. I always was taught the 3% rule also, but in reality you are doing fine if they'll actually eat around 2.5% of body weight per day.
I have my own feed mixed - my "grower ration" is slightly lower fat% and higher fiber% than most commercial show steer finishers (i.e. Purina).
A lot of steers won't eat the extra corn XBAR is talking about late in life when they are almost "done". That's where the supplements come in. I've dabbled with quite a few but all I really use anymore during the summer are Surechamp (on all of them) and sometimes the old trusted Calf Manna (usually on ones I'm holding).
In the fall or winter when you are trying to get one really fat (you ain't there yet), that's where fat supplements come in. Most of the ones on the market aren't the snake oil that supplements that are supposed to help with other "stuff" are. Purina's are great. "Who" makes them often tell the tale on where there is any validity to them. If most of this stuff made by small companies really worked, one of the big guys would have bought them up.
I can't envision needing one other than Power Fuel, especially if you can't get one to eat quite enough finisher. It is what I always use unless I have one with a tendency to bloat in which case I'll use an oil.
If you have access to Purina products, go buy their finisher - but you may need to give them a little prairie hay or low quality coastal at night to keep their belly working right this time of year.
"Look" is more important than pure rate of gain in most show steer scenarios. Most of us that feed lots of them turn calves out on round bales at night to keep the belly and roundness in them that you need. Personally, I use my own feed + either round bales of wheat or coastal hay and cruise right on where they need to be with real gains between 2 and 2.5 pounds a day over the course of a year.
One other word of advice. I let a calf grown into what he's meant to be - I don't try to force a medium wt to be a heavy wt, etc. It's splitting hairs somewhat, but if you have a smaller framed calf let him finish at the weight where he needs to be.