So is it safe to say that if I go with a 7/8” bore size it’ll be easier at the pedal?
Yes, but... There's always a "but" though, right?%)
Although I believe that 15/16" and 1" would be fine, the 7/8" might be a bit small. Not from a power standpoint, but from a soft pedal standpoint.
It's another circle dance, where one thing effects another. Too small a bore will move less fluid, which means the big piston disc caliper needs more pedal travel to get the fluid it needs.
In this case then, a stock size master is your best bet. Whether that was 1" for your year or not, the stock size works very well, as I can attest.
I'm still using the first replacement master cylinder that I put on the Bronco when it had drums in the late seventies. I'm sure by now with all it's sitting, it's not long for this world, but the point was the one I had worked fine for years.
Good firm pedal in fact. Hardly even noticed the slight increase in travel. It was VERY small.
Or would the increase power be so nominal it would be hard to tell?
No, you can tell the difference in 1/8" increments. The more sensitive you are to this stuff, and/or the more you drive a rig, the more easily you will feel the difference. If you don't drive it as much (maybe in your case?) it might be a bit harder. But you can feel the difference in both power needed for a given amount of braking, and the distance the pedal travels.
Neither is a bad change if you stick with stock size master cylinders though.
I’ll be running the same tires (30” BFG ATs) and have already noticed a HUGE decline in brake performance and take off (running 3.50’s). They aren’t light tires

.
Yep, heavier is harder to stop for sure. And harder to get going!
But they're a great size to give you mucho leeway when designing the brake system. Just make sure you take into account any potential future changes.
I ran mine with 32" then 33" tires and they stopped fine for an old truck. Not at all well by today's standards probably, and certainly pushing the limits where with larger tires I would have wanted more power. But better than the old drum brakes ever did. The discs were not a huge increase in power per sé, but a vast improvement in stability, consistency, tunability, control and ease of servicing.
So totally worth it. Even without the booster.
If I was going to be running consistently with 33x12.50 or larger tires, I would consider either a booster of some kind, or a larger brake type.
Paul