Core 2 Duo? You're aiming way too high here. A RISC-V core that can compete with a Cortex A9 or a Snapdragon 820 would be exceptional.
caveat of course: the L1/L2 cache power consumption isn't included in that figure, but, crucially, with the Compressed Instructions reducing cache misses by 20-25% that's equivalent to having approximately double the I-cache size.
basically by a fresh start they're on to a winner.