Dunno if this helps but my rx360 on my 2500k gave the following temps:
1.35v - 4.6ghz - 63c
1.3v - 4.4ghz - 53c
I have 2x 120mm fans pushing and 2x200mm fans pulling, rad is mounted on top of the case. I found with the rx360 adding an extra fan made no difference to temps for me, but my fans are only running at about 600-800rpm, need to buy some gentle typhoons and a fan controller
I am also running the stock TIM which I found very hard to spread and heard it isn't the best.
I have my block mounted horizonally, shouldnt matter which way.
Make sure you have no air in the system... I put my case on its side 2 days ago and a huge air bubble came out filling a whole tube!!