A few logistical tips for those planning their RRW adventure:

Leaving a car at Drymen may be trickier during the last weekend in May (when I went) due to the Drymen Show, which takes place at the showground where the A811 crosses Endrick Water. Even at this time, it should be possible to find some street parking by going into a residential area away from the main road through the village.
Also during the last weekend in May, it is the Strathyre Music Festival. This means you will get lots of good music and stalls to look at in Strathyre village centre when you arrive, but also that accommodation anywhere around Callander and Strathyre will be in short supply.

Accommodation between Killin and Aberfeldy is almost non-existent, so this is the first thing to plan, unless wild camping. The Ardeonaig Hotel on the South Loch Tay road was closed (on 30th May, 2016) and had a note in the door saying it was being refurbished and should open under new management in early June, but it did not look near to completion. Ardtalnaig has no accommodation. Staying further along in Kenmore would entail a significant detour with much descent and reascent after a very long day’s walking. The solution for me was a nice little B&B en route in the hamlet of Acharn – Haugh Cottage, owned by the kindly Mr & Mrs Nicol, who drive guests to and from Kenmore for their evening meals. This overnight stay was the keystone to the entire trip.

Getting from Pitlochry back to Drymen is a bit fiddly but, assuming you leave at 5.30pm on a weekday like me, it can be done like this:

You will need to get a train from Pitlochry to Stirling. From the platform nearest town, take the 1732 train for Edinburgh as far as Perth, but instead of buying one single ticket to Stirling (£19ish), buy one single to Dunkeld & Birnam and another from there to Stirling (£14ish combined) – it makes no difference to your journey and is just one of the peculiar foibles of Britain’s railway ticketing system. At Perth, cross to platform one, being careful to use the main footbridge and not the smaller old one, and take the next train marked Glasgow as far as Stirling. The connection time in Perth is about nine minutes, unless your first train is a little late like mine. If you get a different train at Pitlochry, you may not need to change at all. Leaving Pitlochry at 1732, you should get into Stirling at 1843.

The next leg is a bus from Stirling to Balfron. The bus stands are on the left as you walk out of the station towards the city centre. The next Balfron buses will be at 2010 (£5.30 and goes via Aberfoyle) and 2030. They are both operated by First Bus and timetables are on their website. The buses will leave from stand 11 or 12, and they are service C11 and B12 (or similar). If you have over an hour to kill in Stirling and don’t want to walk too far, you can get a cheap meal at this time of day by crossing the dual carriageway from the railway station, going up the short road opposite and turning right for a selection of fast food joints and chain pubs.

While you’re waiting, try to book a taxi from Balfron to Drymen. I got Clachan Cabs of Balfron, arranged to meet them by the Co-op where the bus stops in Balfron, and the fare was £12. Most other taxi companies seem to be further afield, nearer Glasgow or Stirling, so you would incur a big charge from them. If you cannot sort out a taxi from Balfron to Drymen, you could alight the bus at Balfron Station – a few miles from Balfron, the nearest point on the bus route to Drymen, and with no actual railway station nowadays - and walk along the road, but this would be about six uncomfortable miles to endure. You could try to stay overnight in Balfron, as I think the inn has rooms. Or you could stay in Stirling and try the following day.

Anyway, good luck!