Well the noise levels seem acceptable in those shots although the grey in the background does show some evidence of noise creeping in (either that or its just the colour/finish/material of the shed). As you say it is difficult to tell from shots shown at this size.
However as long as you are happy with the results and more importantly, your customers are, then you’re on to a winner
I wonder if it really matters what people say about the differences in the perceivable noise levels of the Nikon Vs Canon cameras though as you have a Nikon and shoot in that location while I have a Canon and don’t…what I am saying is that unless you have the choice of shooting the same subject at the same time with both cameras side by side to judge the results objectively then the argument is mute.
You can claim yours is better while I could claim mine to be the best…but who really cares as long as we are both happy
Off topic slightly but looking at the pictures I notice that on the whole the horses and the riders are sharp but the ladies face is blurred in both shots, also the leading hoof in the first shot looks like it has been badly cloned into the photo…I am sure it hasn’t but to the uneducated equestrian viewer it definitely looks strange.
What were your settings and how were these processed?