Hi reventon, thanks for your reply.
OK, I left Memtest86+ running for a very long time, went through 7 passes and a bit more and found 0 errors.
No errors with Prime95 for SmallFFT test, everything passed. I'm currently running Blend still, so far no errors or fails, will report back when it has finished.
I haven't got a CD to use to burn for HD Diagnostic, so I downloaded what was advised in the first step: HD Tune. I ran the (full) error search on my SSD and 2 other drives on the CPU and there was 0 errors.
I also did another test using Data Lifeguard Diagnostic for Windows since 2 of my storage drives are WD. All passed with a green tick. Also a step in HD Diagnostic.
I ran Windows Memory Diagnostic and Chkdsk as well, they both returned with 0 errors.
I still have to report the results of the Blend test, but so far, it hasn't picked up anything.