You're quite right about the other two slots appearing as unusable, I still want to test this but unfortunately I can't borrow the other RAM sticks for at least a week due to other commitments; I hope to get round to doing this purely out of curiosity though.
As it stands, I have decided to finally build a new system. As you can see from my previous Speccy posts I am running a 10-year-old machine which I've upgraded to its furthest limits (almost). I have on my desk an ASUS P8Z77-V LK motherboard and I am virtually decided on buying an i5-2500k to go with it in the next few days (unless you would dispute that choice). Right now I'm trying to decide which PSU, (I'm thinking it should be circa 850 Watts) case and cooler (air, liquid?) to invest into, bearing in mind that I already have a decent GPU (Gigabyte R9 270), an HDD and SSD, low-grade RAM, old-school IDE optical drives, (SATA-to-IDE adapters necessary) OS and peripherals.
I will need to upgrade the RAM (to 1600MHz ideally) after I get the system built, so I guess I'd put my budget at about £200 for these 4 items (PSU, case, cooler, RAM) unless you think that budget is unsuitable. This will preferably be a gaming build with a viable upgrade path, so I don't mind making a variation to the budget.
As ever, any advice you can provide would be much appreciated I'm sure I could research and build the system myself, but it's always beneficial to have someone else with experience give a second opinion!
P.S. Should I create a new topic as this is a new build, or should we keep using this one?