The default Strfry config has the following:
# Maximum records that can be returned per filter
maxFilterLimit = 500
# Maximum number of subscriptions (concurrent REQs) a connection can have open at any time
maxSubsPerConnection = 20
It's located here: https://github.com/hoytech/strfry/blob/master/strfry.conf
I don't know how many relays are rocking the default (I've bumped mine), but perhaps it's good to consider.