Having read other reports, I decided to ascend from Ruthven to the south, and it must be the easiest way.
The minor road from the A9 to Ruthven goes alongside the Findhorn, past a couple of signposted fishing spots. The first has a splendid wooden bench on the theme of fishing (see photo). The second has a long parking/passing place where I tucked my Smart car carefully, leaving plenty of space for other vehicles still to use the passing place. That is 500m from the house at Ruthven, though there is also now a huge flat area only about 50m from the house, and it must be possible to park there without being in the way - perhaps best to ask though.
The track is in good condition and easy to follow, with mostly gentle ascents - I was able to run nearly all of it. The track goes alongside the little artificial loch at NH 814338, which is populated with water fowl. Follow the main track all the way to NH 813374, just after the short ascent after crossing the Allt Odhar, where an overgrown (and mostly soggy) ATV track can be found heading ENE then NE. The adjacent land is tussocky but mostly dry. At NH 81843773 a faint path crosses the unnamed stream, just where three little wiggles are shown on the 1:25000 OS map, and actually then goes all the way to the summit, though it is faint and often wet. Even if you lose it, simply ascend just W of that unnamed stream to the trig point. There are only a few peat groughs and they can be avoided. The summit is a bit dull - more like the Pennines than the Highlands. The most interesting thing there was the creme egg I'd carried up.