I have an Orkney Robertson in my tree.
William Robertson "of Firth" married Jean Smith in Deerness in 1889. I descend from one of their daughters, so no direct y-dna link is possible, and I do not know of any male-line descendants.
William is 66 on the 1821 Deerness census, so would have been born about 1755.
There is a Wm born 1755 in Firth&Stenness to Wm Robertson and Margaret Leith.
Do these names/dates suggest a link to your Orphir Robertsons?