I’m planning on bumping ram to the 6 gb max. How much benefit would I see? Does it give me that much more headroom? I know the mem is cheap on eBay, but wondering?
Look at it this way: a bump from 4GB to 6GB gives your Mac 50 per cent more RAM headroom to work with before tapping into virtual memory. A bump from 2GB to 6GB gives your Mac a 200 per cent more RAM to work with.
I upgraded my early 2008 MBP from 4GB to 6GB around when I set it up to run a patched High Sierra alongside Snow Leopard. The bump-up in memory certainly helps when watching a YT clip in 1080p or making a Signal voice/video call, or when working in applications which enable you to sequester or reserve RAM solely for that application (e.g., Photoshop).
With newer versions of macOS, these systems also benefit slightly from the way the OS compresses active memory previously requested by an open application, but not needed in that moment (such as an open application which is in the background, but hasn’t been used for a bit).
So yes. Going 2+4 on these Penryn and Santa Rosa-era Macs is worth it.
Also, with respect to booting from USB2, versus opening your Mac to put the SATA SSD inside on the SATA bus, the difference in read/write performance will be noticeable — and not by a small measure. You’re basically going from a theoretical 480 Mb/s with USB2 (not including the usual USB overhead, which often cuts that down to something closer to 300–350Mb/s), to a 1.5Gb/s SATA I bus (or, as some Macs in the 2007–08 window quietly offered, a SATA I/II bus (with a 3.0Gb/s throughput).
So, at minimum, you’re doubling, if not trebling read-write bandwidth/pipe for your boot/main drive. You will feel the difference. Between maxing the RAM and moving the SSD to internal, it will feel like you’ve levelled up to a much faster, if not a more modern-feeling computer.
