I think saying 8 A57 cores at 2ghz is anything close to x86 at 3.5+ghz on 4 cores.

Clock for clock, pipe for pipe (15 stages in A57, 14-19 in Haswell) x86 still wins because of per-instruction operand volume.

Though i wonder how well this chip would perform at 50w. Double the watts, maybe another 1.5ghz, might be viable for a cheap htpc.