usual question - disc or 50 rear

So its only just over a week to the Vitruvian triathlon so I need to start thinking about wheel choice. The question i am asking myself is does the extra weight of the disc balance out over the advantage it will give, specifically thinking about pulling it up the ripple on the second lap? I am not sure so will have to have a think. I am swaying towards the cosmic carbons front and rear but as a strong cyclist could I drag the disc up the ripple on the second lap, and if so will I lose any time compaired with that gained on the rest of the course. I'm not really fired up for the vit at the moment as unlike Sags my swimming has taken a real hit. I had 12 days out of the pool whilst on leave and since then it would appear that my swim fitness has packed its bags and left for the year. Also during that 12 day period I only ran 3 times, and cycled twice. It was nice to have a break and spend some time with Anthea and Beth, we went to Germany and Belgium camping, followed by a few days in the Isle of Man at my mum and dads. Whilst over there I did get roped into a mountain bike race using my sisters spare bike. Now that was a hard day at the office. It was 85% single track with loads of tree roots and extremely technical, something i struggled with to be honest and the cadence/gearing needed for this course was crazy. To give you an idea of the difficulty of the course it was 3 laps of a 6 mile circuit and it took me 2 hours 40 minutes to finish!!! On the last climb my legs went with just 1/2 a mile to go and I lost a place dropping down to 10th. As a result of such failure I gave the bike to my dad to take home for me and I ran home to punish myself for not being good enough. I hope i perform better in the Isle of Man End to End enduro race the week after the Vit but the course is less technical with more open fire tracks etc with a chance to get the power down.