By the way, after swapping out the fans both card are running around 30-35°C, right up until I start playing Trove. then the card that holds the Trove window shoots up to 60-60°C - Not horrible, but hotter than I like.

That same card over here is over $200USD, but it would certainly handle my needs. Thanks, Freddy.

http://www.newegg.com/Product/Product.aspx?Item=9SIA4UB20U6181

To my mind that temp is perfectly ok 

When gaming in FO4 and W3 my temps go up to 70c on the GPU without a problem and AMD themselves say you are fine up to 80c.

Stick with what you have Dave, if you are only going to be playing low graphical demanding games.   

If you only get the random artifacts popping up while gaming then you could underclock the cards to help stabilize them for a bit.

From what you are saying though it does sound like one of the cards might be faulty, unlikely to be both, one would think.   

Well I've swapped the locations of the cards due to how the jury-rigged fans are mounted, so we'll see how it goes, but I haven't had much time for gaming of late, so I haven't noticed anything yet. Again, we'll see.

The Black Friday deals have already started here Dave - I guess it will be the same over there. What used to be one day became two, then a long weekend and now a week it seems. But now is the time to look for deals

I thought it was probably like that.

I think I am about to splurge £340 on a GTX1070 I just found. 

Went for Asus in the end : https://www.asus.com/Graphics-Cards/TURBO-GTX1070-8G/

Picked up for £340 and got about £20 in Nectar Points as eBay are running a 10x points offer. So £320 in the end.

Read a few reviews on NewEgg first and some others, which were positive. Was a little concerned about the single fan, but I do like these exhaust cards so most of the heat will go out the back. My case is well ventilated for any heat remaining, reviews said they don't get too hot - around 70C on average. Also has two HDMI ports so I will be able to dispense with the adapter I had bought to run Rift and just plug it all into the card.

Right I am done spending !