unless you're considering using an egpu, thunderbolt is completely irrelevant to whether the machine can drive two 5k displays (from any mfg). thunderbolt is saying little more than the device can route pcie signals externally. on top of that, thunderbolt is only available on the intel model

both intel and amd models use their respective igpu, so it's unlikely you're going to have a pleasant experience trying to drive those displays without an egpu