Hi,
An optimally short chain is a racing weight weeny type of thing.
In reality its best to have a medium to long chain.It will last
a little longer if longer, and if you get any problems with
the chain and carry a chain tool, you can remove the
problem link or links without any real issues.
FWIW dropping 7 teeth is removing 3 outside links.
rgds,sreten.
AFAICT my chains are nowhere near as short or long as they can be.
That is my rear derailleurs never approach horizontal, they both have
loads more capacity than my gearing needs, and for both the cage
of the derailleur is around vertical for the middle gears.
52/42 with 7 speed 14-28 and 48 with 6 speed 14-28 and 20" wheels.