Well, the 40 seemed to run fairly well on this, its first day, although the distinct lack of passengers could've helped. We managed Aberystwyth to Carmarthen in two hours and one minute on the 0900 service this morning and a right-on-the-button one hour 55 minutes on the ex Carmarthen at 1520, although I suspect we were greatly helped by not having too much of that pesky "stopping to pick up passengers" malarkey.
Things seem tightest, though, between Pencader and Carmarthen. On the way back, we managed to make that up by the time we'd reached Aber (no mean feat, considering that we were already six minutes behind schedule by the time we passed West Wales Hospital), but travelling to Carmarthen, having done very well as far as Lampeter, things started getting tight to the point of not really working too well at all. By the time we reached Carmarthen, the driver was already five minutes late starting the 1100 return service, bless 'im.
In short, I'd say you could divide the new 40 service into three parts, thus:
Aberystwyth to Aberaeron: should be enough slack to run on time even with more stops being made along the way;
Aberaeron to Pencader: very tight, but just about do-able;
Pencader to Carmarthen: no chance, to be blunt. We only stopped to pick up a couple of times and we still didn't manage it, so goodness knows how it'll go when there are actual passengers around.
So, a fairly successful first day, really, but the real test's going to come when the buses - and the roads - fill up during the week.
Our bus on the way down to Carmarthen, I noted, had had the "5/X5" stickers hastily removed from the window next to the door, betraying from whom it'd been pinched to plug the gap until our double deckers arrive, although on the way back our bus (both Pulsars, by the way) had a poster for somewhere in Knowsley on display, so clearly they've been gathered up from all over the place.