Theoretically x86 could be more efficient in terms of instruction caches and memory bandwidth, but it doesn't seem like this would be very substantial in most use cases. I'm not aware of many hot path instruction streams that are so complex that caches and interconnects are getting saturated.

Moving instructions to the decoder is way more expensive than actually decoding them. The factor is insane once you get to DRAM. But, it doesn't seem all that relevant in practice.