I don't know that a switchback is going to be any better of an answer if you are running big steam. The tail tracks of each switchback - where the train has to fit while the turnout is thrown to go up the next grade - has to be long enough to fit the entire train. If you have multiple switchbacks, each end of the grade has to have the train length tail track. Tail tracks for long trains will take away from the run for your grade significantly.
Let me give you a small example from my layout plan. There are 2 switchbacks on an 8 ft long layout section. I have set the tail tracks at 21" long - a very short train, 2-3 cars and a tiny engine. Allowing 9" for the turnout before the grade starts gives a whopping total of 36" to climb 2" on each switchback. (96" - 2*(21"+9")). This means a 6% grade before easements. With easements at each end, the peak grade ends up at about 8%. With the 2 switchbacks, I have gained 4" in 8ft at the cost of 21" trains and 8% grades. Which is fine for a backwoods narrow gauge line, but not very good for Class 1 railroading.
When you add the space for the tail tracks in, you can probably gain just as much if not more vertical distance at a reasonable grade without the switchbacks as you can with the switchbacks. You would have to 3 or 4 switchbacks to do better.
Next issue with switchbacks - is your trackwork and rolling stock good enough to handle backing through turnouts and up or down grades flawlessly? Helix trackwork needs to be bullet-proof; switchback trackwork even more so since 50% of the time you are backing up.
Last point - to many folks, switchback operations are even more boring than grinding up a helix. And unlike a helix, you can't just set the throttle and wait. The turnouts have to be thrown, and the train stopped, reversed, and started at each switchback.
Just some thoughts you might want to be aware of. Real railroads avoided switchbacks whenever possible - for a reason.
I'll post some pix next time.
to find the right formula which is as followes:
