I can fully understand what you mean about 'a struggle but worth doing it'. I've never attempted this particular route, but on the one hand I have encountered the sort of navigational 'challenges' you describe and on the other I've encountered some fantastic remote scenery in those areas of mid-Wales.
Actually, if anyone reading this is a 'multi-disciplinary' outdoors type then I'd wholeheartedly recommend doing Wales coast to coast by bike - the Sustrans Lon-Las-Cymru route is excellent. I took a week over it in May three years ago, camping and taking the off-road sections where available, and had a fantastic time. We omitted Anglesey but went from Bangor to Chepstow (there's a Cardiff finish too).
I recollect Barmouth as a happy place - chance for a grand cafe breakfast having come down from the Rhinogs and before crossing the estuary and tackling the hills west of Cader Idris. The route continues to Machynlleth and then under Plynlimon to Devil's Bridge, and on past Strata Florida to Llanwrtyd Wells - we ducked out of atrocious weather to Dolgoch youth hostel which was a great out-of-the-way bolthole! In fact checking for Llyn Brianne on the map just now that must be the one Cath refers to. We were the only people there apart from the volunteer warden. Unfortunately I believe it's on the YHA's closure list - due to go in Oct 2007!
From Dolgoch we finished in a day and a half, via Hay on Wye, over Gospel Pass, down to Abergavenny and over to Chepstow - I think we put in a 70 mile day because the route over the Black Mountains felt so flat in comparison to what we'd already done!
Anyway sorry to go a bit off-topic, and I don't suppose that helps you much Chris, but your thread brought back the memories for me - thanks :)
Edited: 24/10/2006 at 22:01