the bigger the gap, the better the burn will be, however there is an issue with the coils on the m104 and whether or not they are up to the task of making the spark jump through the wider gaps. i do not remember the specifics but there was a caution about going overboard with this. 34 or so should be ok...
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"