Did not turn out exactly as planned. Basically I dragged myself out of bed in the dark, got my gear and bits together and headed off. I was 20 mins into the spin to work (past the point when you're asking yourself 'why am I doing this?') when I realised I left my bottles in the kitchen. Without those I was not doing any long spin home. So I turned around got home and had a quick shower before heading into work in the motor.
Pegged it back and was out on the road at 2pm. I basically did the usual big spin, but in reverse - Blessington, Laragh, Sally Gap, Glencree, Tallaght, Rathcoole and home. Did it non stop this time which was nice. In total it was 112kms with almost 1000 metres of climbing in 4 hours 10 mins. I spent almost half the spin at 80 % max heart rate or greater. The weather was perfect - some sunshine and cool. There was a breeze but it was nothing to write home about.
I did the spin with 2 400ml bottles filled with a Torq engery/Glucose mix, one Torq bar and a Torq gel (I only used it as they have a best before end date of December!)