I think forge has to work on optimization and further support on optimization mods (this might sound like a complaint it's not though)
I tried out a ftb sky adventures and i could not play it often lag spikes like every 30 seconds
and all of good optimization mods that are really good just are discontinued now because of forge
ex. phosphor, TexFix, and betterFPS
and mods in general hit hard on new/weak computers