Which one of these will be more powerful? I have two scv4k's going on three tridents but I have a feeling I'll need/want more power for those.

Switching to a 5k amp versus a 4k won't be worth the money. Without taking into account thermal compression, you'll need to double power to hear a difference. I would just grab a third 4k,run one per sub on solid electrical and call it a day, but like I said, won't hear even that difference.

Edited April 17, 201510 yr by SpeakerBoy

So you wanna switch from two 4ks two one 8k, makes senses. I would focus on enclosure and other things then adding a small amount of power.