I've been wondering about this route, too.
I'm planning a short trip through Scotland in July - so I'm expecting long days, and at least a passing chance at moderate weather (hey, I live in Seattle, I'm used to rain, I expect I'll feel right at home).
I'm looking at driving from Edinburgh to Inverness in one day - via Stirling, Crianlarch, Glencoe, and Fort William (basically, M9 to A84, A85, A82 - I think). The idea is to get from Edinburgh to Inverness in a long day, with enough time to stop and enjoy the scenery (moors, highlands, and obligatory Loch Ness sillyness). I'm OK with a long day in the driver's seat (and driving on the "wrong" side of the road) - although I'd like to reach Inverness by dark (we'll get an early start, and it'll be early July). I'm expecting lots of pretty scenery, maybe some rain, roads that are good although not big highways, an occasional slow truck and/or wildlife, and lots of options to stop, stretch legs and take photos - but no real "must see" attractions (except a few obligatory items towards the end of the drive, Nessie, Urquhart Castle, etc.).
I chose this route because I figure it's a reasonable compromise between speed and scenery - Rick's recommended route takes you out to Oban, which I'm sure is nice, but we are not heading to Mull/Iona (we will end up on Lewis, but need to get to Inverness first). I assume that the scenery is nice going over the top from Edinburgh to Glencoe, then we'll complete the drive along the scenic Caledonian Canal. Admittedly we will miss the scenery between Glasgow and Glencoe, but will get the Moors and mountains as compensation.
I know it will be a full day, and a lot of driving through nice scenery. We expect to depart from Edinburgh around 8 am, and hope to arrive in Inverness before dark (sunset is after 10 pm), allowing for occasional brief photo op stops.
I think this is a reasonable plan. Is it?