I think a 2.88:1 would be an ideal ratio for a 300SEL with first gear start.
Low gear ratio would be about 10.9:1 (with ~3.8:1 first + 2.88:1) versus the ~3.47:1 + ~2.3:1 (second) making about a 7.9:1 only.
So you'd be quicker and probably have better economy as the motor won't be lugged badly getting from a dead stop not to mention drop about 500rpm on the freeway... about 2900 @ 70mph versus closer to 3500rpm @ 70mph.
Problem is 2.88:1 was only in the SDLs for the W126 (as I understand) and it'll cost a bit to get a
VB converted for the ~6400rpm shift point. I have a few first gear start VBs but I need them, I see them at times. Next time I have a spare I can take it apart to compare with a second gear start to see what's up.
2.47:1 seems like it'd be too low of a cruise RPM for an M103 in a W126... not enough power to keep it going at 24-2600rpm @ 70mph. But hell, it very well could for all I know.