I rode LEJOG last year (although more slowly – over 10 days) on my Spa Cycles Audax Ti bike. It was perfect, sooo comfy. There were some full on race bikes in the group and I didn’t notice a disadvantage in having a heavier bike (also with mudguards and 28 tyres). Over the day/week we all had strong times and weak times, the ‘leader’ changed regularly… it is about so much more than the bike.
Have to admit I lost the mudguards after crashing in Yorkshire, but the initial advantage of having a relatively dry bum at lunch time far out weighed the weight IMO.
Good luck and have fun – I would ride it all again if I could 🙂