Hi Chris these are some of the routes we've been using over the last ten years.
From Painscastle go up the A470 to Rhayader, B4518 to Elan Valley up to Devil's Bridge, there a nice cafe at the Rheidol Railway Station. Then go South on the B4343 through Tregaron then turn left onto the A482 to Pumsaint, then follow signs for Dolaucothi Gold Mines but keep going up to Llyn Brianne then left through Abergwesyn to Beulah back to Painscastle. You will do all that in one day.
Painscastle to Hay-on-Wye then over the Black Mountain to Llanthony turn right at Stanton to Crickhowll then the B4558 through Llangynidr to Brecon. you could make a detour to Talybont Reservoir there a nice cafe there. From Brecon head up the B4520 then left onto the B4519 which will take you into the Military Training Ground at Mynydd Eppynt. You could then head to Beulah and go round Llyn Brianne the opposite way round, it is well worth do both ways, but keep left for Cynghordy Viaduct
These two routes have some of the best open roads and scenic road that we have used over the last few years.
Two photos of Elan Valley