I beleive this is as shooter-specific a question as ever.
One shooter might be disturbed from the recoil of a .30-06, whereas another shooter may shoot his .375 H&H all day long and never flinch.
Me, personally, I prefer to brake all rifles .300 Win/Wby/WSM or larger. I have 2 .300 Win Mags; one is a custom long range rifle that started life as a Win M70 Laredo, and because of its weight, is quite pleasant to shoot, although she still thumps ya when shooting prone. I have a brake on it, but truly it isnt necessary as it feels like shooting a really loud .243 Win with the brake on. The reason I installed the brake on it was because I wanted the surefire suppressor mount- even though Ill probably never get the cash to get one.
My other .300 is my lighter-weight medium-long range "mountain" rifle, which I use for hunting whejever Im in steep or difficult terrain. I built it using a 700 action, fluted bolt, 24.5" fluted SS Remington barrel, pillar and glass bedded Bell&Carlson stck (much lighter than my other rifle's stock which has a full length alloy bedding block), aluminum scope rings and mount; this rifle only weighs 8 pounds with it's Nikon Monarch 4-16x42 1" scope... it definitely smacks you good when shooting prone, but bench and offhand is fine. When I built this rifle, I was out zeroing and breaking it in - I was used to scopes with more eye relief than the Nikon, so I got scope kissed pretty good - I decided then that this girl is gonna get a brake lol.
I also like to brake all my auto rifles - for fast follow ups; nothing to do with recoil/flinch.
Its better to be safe than sorry; once you develop flinchitis, it's a pain in the butt to get over... I have trained several shooters who buy the latest and greatest uber-mag, and then have to re-learn the fundamentals of markamanship because they are scared of the recoil.
Sorry for all the typos, Im using my phone for this.