Lamboy
You're faster than you think. Your 4.2m is at 8:24 (well under 8.5 mins :-) ). To put that into context, at that pace you'd do a 10k race in 52:02 - check out some race results pages & you'll see just how respectable that is especially given that yours includes hills.
In terms of where to go, it really does depend where you want to go. You've already got the basic legs so how about finding a flattish 10k to aim for - I did one yesterday in 51 mins so you're already not far behind me.
Do you keep a simple log of your runs, I find it realy useful to keep as it motivates me when I don't feel like going out (the blank date field glares at me) and also when I look back at how far I've come in a relatively short period.
Good luck
Nick