Q: Should I choose 1.5V or 1.35V?

if its a late 2012 or earlier can can upgrade the ram

only buy good mac compatible (macs are fussy when it comes to ram)

http://eshop.macsales.com/shop/mac-mini/

So would you suggest it wise to purchase CL-9 grade instead of the more common

and slower CL-11 grade, as part of an upgrade in memory specs, for Late 2012 Mini?

And if the processor is a 4-core, it could help to use faster latency given most of these

Mini Macs shipped with rotational 5400-RPM hard drives, in-chip speeds are essential.

{Server models have two 1-TB rotational HDDs; there's a source of potential bottleneck.}

While some suggest one brand over another, the benchmark specifications within the brand matter.

http://www.memorybenchmark.net/ram.php?ram=Crucial+Technology+CT102464BF160B.C16 +8GB&id=1921

Good luck & happy computing!