1 pointI don't think the heatsink you mentioned will work, the R5 has a slightly different dimention, a 4th pipe won't fit on top. I don't know what the experience is from other users but the heatsink I bought from taobao gave me a 12 degrees drop compared to the stock heatsink (tested with mx-4 thermal paste) after that I applied the thermal grizzly liquid metal which gave another 15 degrees drop.
1 pointSounds like a lot of effort with a lot of risk. Personally I bought this heatsink from taobao through yoybuy. The heatsink with the m14x fan mod and liquid metal from thermal grizzly keeps the temps easily below 85 degrees with a 4.5 overclock on all 4 cores.