I think sub 3 is perfectly possible with a 1/2 pb of 87 or 88. That being said, I think that there is a lot to be said for getting used to running faster. I started doing the local park run last year. I got down to 18.30 ish which is just under 6 minute miling. After this running 6.30 feels comparatively steady, and late last year I knocked a couple of minutes of my 1/2 pb (83.02), and that was with a marathon still in my legs.
Anyway bunged up with cold so only writing about running this weekend! Happy running everyone!