limit find output AND avoid signal 13

Since you're already using GNU extensions (-quit, -H, -m1), you might as well use GNU grep's -r option, together with --line-buffered so it outputs the matches as soon as they are found, so it's more likely to be killed of a SIGPIPE as soon as it writes the 6th line:

grep -rHm1 --line-buffered pattern /path | head -n 5

With find, you'd probably need to do something like:

find /path -type f -exec sh -c '
  grep -Hm1 --line-buffered pattern "$@"
  [ "$(kill -l "$?")" = PIPE ] && kill -s PIPE "$PPID"
  ' sh {} + | head -n 5

That is, wrap grep in sh (you still want to run as few grep invocations as possible, hence the {} +), and have sh kill its parent (find) when grep dies of a SIGPIPE.

Another approach could be to use xargs as an alternative to -exec {} +. xargs exits straight away when a command it spawns dies of a signal so in:

 find . -type f -print0 |
   xargs -r0 grep -Hm1 --line-buffered pattern |
   head -n 5

(-r and -0 being GNU extensions). As soon as grep writes to the broken pipe, both grep and xargs will exit and find will exit itself as well the next time it prints something after that. Running find under stdbuf -oL might make it happen sooner.

A POSIX version could be:

trap - PIPE # restore default SIGPIPE handler in case it was disabled
RE=pattern find /path -type f -exec sh -c '
  for file do
    awk '\''
      $0 ~ ENVIRON["RE"] {
        print FILENAME ": " $0
        exit
      }'\'' < "$file"
    if [ "$(kill -l "$?")" = PIPE ]; then
      kill -s PIPE "$PPID"
      exit
    fi
  done' sh {} + | head -n 5

Very inefficient as it runs several commands for each file.

A solution to avoid the errors could be this:

find / -type f -print0 \
  | xargs -0 -L 1 grep -H -m 1 --line-buffered 2>/dev/null \
  | head -10

In this example, xargs will stop once the command fails, so there'll be just one pipe error, which will be filtered by the stderr redirection.