Should i start replacing the cat 6 between the ISP Router, SonicWALL, and the main switches to SFP+ fibre connections, or will cat 6 still have enough bandwidth?
Não.
if cat 6 is still ok for the job, at what point would you upgrade to sfp+?
Quando você precisar mover > 1Gbps (na realidade, passaria para o SFP + quando estiver lidando com cerca de 550-600Mbps, mas isso é porque eu sou um geek)