INTRO:
BSD, my first machine and still love it a lot! The simple rules mixed with a very challenging gameplay and the beautiful gothic romantic atmospheres, the perfect music and sound effects, makes it one of the very best.
I experimented a lot with this machine, in terms of setup. I tried all sort of adjustments over the years. So here are my conclusions:

In the beginning I thought the machine was too brutal, so I removed lightning flippers for normal ones. Quite a big change, now the game was more enjoyable: I started to achieve more goals and have more fun, and score big sometimes.
I then reduced the sensitivity of the slingshots: that also helped a lot with the ball being much more controllable and stoppable on the flippers, keeping the gameplay more under control.
Still, I was far away from the top scores I read here on the records page. So I decided to reduce the ANGLE around 5 degrees and that definitely was the most important move! Suddenly I started achieving triple jackpots quite often, jackpots all over the place, sometimes even reaching the max (480/300 millions) and my scores grew very much. I played like that for months, until.... I turned the machine over! Around 14 billions or something.. most games lasted forever, very often into few billions. in the end I often started to play the first ball and then.. switch off the machine, bored. The interest was gone. BSD became almost similar to many other easy games out there. No good.

So, in the end, I am back from where I started. Lightning flippers are back, the angle is as recommended around 6.7. I still quite like having the slingshots not too sensitive though. Now achieving a triple jackpot is a real challenge, it happens very rarely. The adrenaline is pumping again in those moments. Big jackpots? Cant see them in a while..
But THIS is BSD! BSD is a very tough game. As a beginner or intermediate player is needed to reduce the default difficulty. But when you are an advanced player, standard (or near standard) setup is fine.

THE POINT:
We often discuss how hard or easy a game is. I understand that those discussions are relative to the default setup (or at least they should, because I think that many disagreements depends on different setups). But anyway I think in general the power of adjusting the setup of a pinball is usually immensely undervalued or even completely forgotten. It's possible to turn an easy game into a bitch or an hard game into an easy one (as in this case). Maybe it depends from commercial reasons: better to push people to buy a new "harder" or "easier" game, before the owner uses his brain and adjust the lovely machines he already owns first. Having said that, it' nice and fun to change lineup of course! But I think people should play around more with their machines before looking for something different: just play around with the angle and you'll have new games instantly! I heard quite a few people saying they sold a machine because they did not like it. I asked: "did you try changing the angle?" the answer is always: "no". Incredible.

I can' t understand your reasoning. You say it depends from production era But also owner choice. This is contradictory. In your White Water review I read you set it at 11 degrees...

For me its up to owner's taste really.. Then of course on average certain generation of pinball machines play - on average - better at a steeper angle than others.

Ok, I see your point.

According to my testing one or two degrees already makes a big difference. So the ranges you provided for different generations of pinball machines (I would add + or - 0,5 degrees) provide a perfect space for adjdustments for personal tastes, respecting at the same time the original setup that designers had in mind.

Still, I repeat my idea: play around with + or - 1 degree (from the recommended/standard angle) and you will be impressed on the results. The game changes quite a lot.