From the past, how things have changed: in an old book by Sam Snead on driving, in the 'pick the right equipment' section, he suggests that if you drive it 200 yards you should use a club with a regular flex staff and a swing-weight of C-4 to D-1, with about 10 degrees loft; and if you drive it 225+ yards, you can go with a stiff shaft and a swing-weight of D-1 to D-5, and as low at 8 degrees loft. That's it: that was the line of demarcation/the distinction back then between a good amateur and the only other category that Sam mentions, the pro.
Okay, from today: good article with Tiger Woods discussing his old and current equipment and equipment testing etc. Here's his most recent views on this topic: “I am of the opinion that we should bifurcate. The line of demarcation, in my opinion, should be professional and amateur. That's it. ...If you're an amateur, you can play the most juiced up golf ball, just go hit and go find it. I think that amateur golf, we can actually push the limits with everything if not get rid of the limits, right. Let them go have fun. Let them enjoy it. Let them — we're trying to bring more people into the game of golf. Let them go ahead and enjoy hitting it further and straighter. But professional ranks, it's like a different deal. It's like going from aluminum in little league and college to when you turn pro and go into A, AA and AAA and obviously the bigs, it's all wood. That's just the way it is. The rules are bifurcated for them. There's no reason why we can't do it for us. Now, then that goes back to do you standardize the golf ball at the pro level, and this is where it's kind of tricky because each manufacturer is going to say, no, you can't, because they want to produce their own golf ball. But you can probably change dimple patterns to make them a little bit deeper, a little bit smaller. You can soften up the cover, obviously soften of the core, make it slower, and you can bring the ball back.”
Interesting aside, re Tiger's irons/specs: "I'm stock spec from say the 60s. The only thing that would be weird is I have a 60‑degree sand wedge....But yeah, my pitching wedge is 50 degrees, my 9‑iron is 45 and a half. I see some of these guys with pitching wedges that are 45 or 44. This whole four‑wedge system I don't understand; just why don't you take something off? I just don't understand that part. In the Bahamas I had 89 yards out and 95 yards out and pulled out pitching wedge. To me that's what I've been able to do. Let's also don't forget I play a softer, spinnier ball, so those little shots are easier for me to hit.”