Not quite. The first bit - ride out to Cardiff to do the FNRttC - then I'm going to stay over in Swansea and have a pootle further out west to Pembroke on the Sunday, and get the train back from there. I think the others are just doing the ride out to Swansea and train back.
Its about 150 miles from my place to Cardiff. Plus 70 for the ride, will give 220-odd to Swansea on the Friday day / night. It's probably 20 miles further from your place, so would be 240, but we're all west so planning to meet at Harefield rather than HPC (although it has to be said there is something in preserving the tradition of HPC starts for FNRttC...)
But riding back would be 440 for me (and 480 for you)

. I think that would be a bit far for me. I'm already doing 600k / 375 miles the weekend before and I don't want to bite off more than I can chew (and end up having to hobble onto a train somewhere with tail between legs and everyone saying 'I told you so...')