The values to experiment with are LINES (you have it set at 100) and READAHEAD (you have it set at 32xxx).
The READAHEAD is the number of bytes cached for each LINE. So 100 x 32xxx bytes = ~3.2 MB. And for 15 partitions this would indeed total ~45MB.
SFSConfig dos not make any permanent changes to disk, that's why it needs to be run at every startup. So you can change these values at any time and it won't damage anything (well I haven't killed my HD yet). I guess the usual precautions apply.
So I guess you'll just need to experiment to find the optimum speed increase for the memory you're willing to give up.
Use SFSQuery (or SmartInfo from Aminet - nice GUI) this will give you info on 'Cache Accesses' and 'Cache Misses' which might help in deciding reasonable values.
Hope this is of some help, and I apologise if you knew this already (I may have misread your post).