Hi Kate, I have run it twice and saw a pacer in 2012 but none last year. That said I wasn't specifically looking for them.
In 2012 I ran 1.53.15 and I passed a 2 hour pacer around halfway. I was running ahead of schedule aiming for sub 2 hours so I reckon they might have set off quicker than ideal if someone was looking to follow them with the aim of dipping under two hours.
Suppose you could always use a stopwatch and monitor your pace to aim for 9-minute miles to run about 1.57/1.58 but other than that I don't know what to suggest.
The pens do make a difference, I started from Orange D in 2012 and ran 1.53.15, last year I was put in White E and although I ran a faster time (1.49.48) I found I was dodging and weaving to ovetake people in first couple of miles. This year they have given me Orange C so I suspect it will be people having to overtake me in the first few miles.
Got my pack through today at last! They have moved me up from White E last year to Orange C this time around. Reckon I will need to be careful not to go too quick early on as pace is bound to be a bit hotter amonst quicker runners but really looking forward to it.