IIRC LB supports microcode updates, but I don't think older CPUs will receive new microcode updates from CPU vendors.

Then again, newer CPUs have a host of other problems, like only supporting platforms where rolling your own boot firmware / UEFI is next to impossible.

Personally I think the CPU has a much lower attack surface than something like UEFI (microcode updates are also pretty tiny), so I would rather have an outdated CPU than an outdated / vulnerable UEFI implementation.