In my case, the actual content of the varchar field is much much
shorter than max field length.

Not sure if I got your point about char vs varchar right. Clearly,
char(10000) is a bad idea. I dind't find char(200) that bad. Quite a
few fields have a size between 30 and 100 in by database and I tend to
use varchar only for fields having a potentially large size.

Reason to prefer char for most fields was performance. I was assuming
that char would be more efficient than varchar with respect to speed.
Is that wrong?
(This is probably something to ask in the Firebird-general newsgroup.)