Re: Sachs cassette Question-HG compatibility + lightest 7 sp
Lightest 7sp will either be a Ti or Alu block. Somebody will have made one.
Of course running an 11-24 over a 12-28/32 and dropping to 20 on the front would make it lighter.
The retro-lightest-notoverlyexpensive is probably taking a 12-28 m900/737 and loosing the 14tooth (iirc, very long time since) and 3mm spacer.
I cannot remember but early 11-28 737's may be able to loose the 11 tooth and fit a 12 tooth lock ring, but I cannot remember the outcome.