Howdy,
I have mSATA SSD for OS/ScratchDisk and 2x 2TB Samsung 2.5" HDDs in a ReFS mirror installed. Honestly, if we're talking about I/O subsystem, the old 4xCore processor and old gen video card (M2200 in my case) do not warrant much more throughput. However, if only 8TB SATA 2.5" SSD (Samsung QVO) were cheaper (as I'd hate to throw a lot of cash into the older tech), I'd be happy to get two of them, split them 1+1 Raid0, 7+7Raid1, and enjoy 1Gbyte/s for programs and scratch space, and 7TB of bit-rot-protected mirror for my data.
There's a better compatible WiFi card (6/7), but again - what is it really providing in everyday computing? At some point I connected my NAS over the WiFi for portability, but it was a) slower than 1Gbe b) not secure. Internet speeds where I am are lower than what original WiFi provides.
There's a "5GBps" Ethernet adapter, that provides about 3-3.5Gbps, in case one has a sophisticated NAS (i.e. Flashstor Gen 2 from ASUS, that has 10Gbe/5Gbe/2.5Gbe ports). That'd be a nice boost over 1Gbps indeed! One may bypass upgrading internal I/O and go straight for a really fast external one, which will be future proof, but not portable, of course.
In raw performance department there's potentially an opportunity to punch real hard with 4050 MXM, but only if it works. The M2200 is significantly faster than original K2100, the 4050 MXM will more than triple the performance again (+250%). But, alas, it is a 6GByte card, so not as cool for acceleration of video/photo editing.
Regards