Great Western Coffee Shop

There will either be 4 of us travelling to Cardiff Central from Milton Keynes on a weekend in May.  I don't know which weekend yet, but we will be able to observe any off-peak restrictions and are quite flexible on time.

I'd ideally want to travel via London to ensure we get a FGW HST to Cardiff.  However, my group are being swayed by the cheaper price going through Birmingham.  Unfortunately, one not being from the UK and the others not regular travellers, they are not appreciating why I may wish to avoid travelling on a Voyager!  I am also the only person with an Oyster card.

On the return, I would like to break our journey at Bristol Temple Meads, so we cannot use advance fares because I don't know how long we will be there.

I've tried all sorts of splitting combinations, but the cheapest seems to be a direct ticket:
MKC - CDF SSR +Any Permitted ^77.00 each, so roughly ^154.00 for the 4 of us on GroupSave 4.
This will force us onto London Midland between MKC and EUS, which also isn't ideal as my foreign friends all have visions of all our trains whizzing along at 125mph and not stopping anywhere en-route.

Are there any splits I could have missed?  I've tried Didcot, Bristol and Swindon.  All more expensive.

Have to considered Cardiff -> Oxford and the express bus?

This works out cheaper than London, but not as cheap as Birmingham.  The rail fare would be ^103 plus ^34.80 for the coach.  One of our group detests coaches (travel sickness apparently) so this wouldn't be ideal.

(Before someone asks, I've no idea how she manages to not be sick when a Pendolino tilts but is always sick on a coach)

You say weekend. Is that out one day and back the next, or a day return?

Out on either Friday lunchtime or first thing Saturday morning.  Return will be on Sunday.

Last time I checked connections between trains from Didcot and the coach at Oxford aren't great, and the coach takes a lot of time to get out of Oxford, calling at Gloucester Green coach station after the railway station.

I can fully understand why you'd want to avoid a Voyager, but wouldn't the route most likely be London Midland to Birmingham, then on to Cardiff by a Cross Country Class 170? Less hassle than going via London I'd have thought.

Journey time through Birmingham is roughly the same as NRE quotes for London (although I seem to have become an expert recently at making speedy London transfers).  For future reference, is BHM to CDF always a Class 170?

I completely forgot that XC also don't accept GroupSave, which will definitely make Birmingham a considerably more expensive journey, even considering LM's online sale.

I might look into Advance fares when we've decided on the date, at least for part of the return journey.

On another matter, is there any way of getting Train Line powered websites to give the ^154 fare?  They all seem to quote journeys on Virgin as they overtake LM, which means they show only ^200+ tickets.

No, and it's getting on my nerves! The GPS4 discount is hidden away in the Railcards drop-down menu but that doesn't do any good because I can't figure out how to get it to avoid VT between MKC and EUS.

Edited to add:
The NRES website will show journey times and the GBP 154.00 fare if you go into the advanced search options and tell it to avoid Virgin Trains, but then when you click on the "buy" button it doesn't seem to be able to transmit the info to a Trainline-based ticket purchasing site. This may be a job for a telesales centre or buying at a staffed station I suspect...  :-\

Yes, put in via Hemel Hempstead.  ;) That'll bring up 2 of the 4 LM services from MKC to EUS per hour (the xx22 and xx47). Nothing stopping you using the xx05 departures which are fast to Watford Junction.

EDIT: And I think you won't beat the Super Off Peak Return (LM+FGW) with GroupSave fare. I've had a look at various options to try and get you and your friends on a Pendolino as well as the usual split points. Nothing doing without increasing the cost. One of those journeys where splitting is only likely to yield savings if it was a Day Return.

That's great.  Saves a trip down to the ticket office to get the seat reservations when we eventually agree on the date.