Kernel Setup/Compilation

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You mean initramfs, right? Ramdisk usually refers to tmpfs for GNU/Linux.

I suspect there is not much to be gained from kernel tweaking as the kernel is not all that resource inefficient to begin with. There are however few things that could at least be tried:
Even on faster more modern systems cache misses are quite expensive and on older systems with slower memory even more so, by trading some code execution speed in order to fit more into caches the overall performance could in theory get better, or worse, depending on workload and the cpus cache setup.
To enable this kernel needs to be patched, but it is a thing and there really is no downside to using it. It is going to produce better code for this particular system, but probably not anything noticeably faster >CONFIG_IOSCHED_DEADLINE
If still on spinning disk JFS+Deadline is still a great combo offering ok performance with really low cpu overhead. In practice this is quite meaningless however as the overhead from disk encryption completelly overshadows any scheduler or filesystem cpu usage

Some basic debugging options or things that fall under CONFIG_EXPERT could also be used to shave off few k of memory usage or code size, but unless it is some embedded system where every k counts it really is not worth the effort