Im in Gold I myself, I dont even use a speed lead for my defense or even when i fight speed teams, (not meaning to undermine anybody's speed ratings whatsoever) but i do use a champion in my hybrid style arean team that usually goes first, with just 266 speed.
Id say about 60%- 70% of the teams I fight my champ goes first.
I have found more success just letting them go first then using a slow nuker myself that hopefully survives everything.
I would say try using different lead champions like HP auraor shield set HP champ to protect your team... usually you can wipe an all attack team with just one AoE lol its just surving until your turn is whats tricky.
I would by all means keep the speed gear you have on your champs currently, even with a defensive/resist /go second team kind of setup speed is still very important you just can breathe easier knowing your team's success isn't singularly dependent on going first EVERY time.