So I posted this mushroom shot which was shot at F8 and a closer perspective and I think the result was quite pleasing with the fungus standing out from the background in sharp focus against the relatively out of focus background. Moving further away from the mushroom at the same f-stop would have caused the background to be less defocussed and the effect of highlighting the subject (mushroom) would have been lessened to a large degree. Here we have the power of a sharp prime coming to the fore because I dialled it open to f2.8 and instead increased the the out of focus character of the background and actually heightened the effect!
The Nikon f1.8 wins again! At R999 (directly converted to US $149 although they go for a mere $100 in reality) this is the bargain of a lifetime! If I had set it to f1.8 the result would have been an even thinner slice of focus but at the expense of a tiny bit of sharpness. The main problem is that very little of the subject (mushroom) would have been in focus and then the effect would have been ruined. So don't be afraid to experiment a bit until you find what works for you.