Well, now I know for sure I am capable of going for 52 miles, having done it (well, 83.7 km to be precise) last night on the stationery bike. It was quite a slog, but I managed it in 3 hours and 57 minutes, which I'm prety pleased with. I did feel a little bit nauseous, but a nice sit down and a KitKat soon set me right!
I'm surprised at how few aches and pains I have this morning - my lower back felt quite tender after a the first couple of hours, and... well, let's just say I'm glad I was wearing my trusty padded shorts! - but I've cycled into work as normal this morning, and am feeling pretty chipper (but still quite tired).