Well:
"When the players got stronger they found that playing with "completely free" rules was in great favour of Black (the beginner of the game). It is also proved that there is a sure win for Black when playing with "completely free" rules."
(from http://www.renju.nu/r1rulhis.htm)
The rule "no-more-then-five for black" is one of "black" restrictions in renju.
(do skréše) Jak chceš vlitnót do špilo se špilošem, keré bode asi tak dobré jak te, možeš zvolet vežadované rozsah BKR v novy nabidce ke špilo. Potem nikdo, kdo do rozsaho nepasoje, toďto nabidko ani neovidi. (Katechka) (okázat šecke vechetávke)