I've just done w7r1 tonight and decided to try a couple of higher-speed intervals during my 25 mins to get myself running a bit faster - after all, I'd already done 25 mins on wk6r3. Hmmmm. Did NOT feel great - I completed the run but my lungs felt they were bursting out of my chest most of the time. (It doesn't help that there are a couple of hills on my route). The interesting thing was that my legs were fine at the end - it was just my lungs - whereas when I first did the 25mins my legs were like jelly when I got home! So I seem to have made some progress - and I did almost complete 3k in my 25 mins, which is more than last time..... But I probably worked harder than at any other time during C25K.
I wouldn't normally be worried about going faster - it's just that I'm doing Sportrelief 3 miles in 2 weeks' time and don't want to be unprepared and have a miserable day.
Any tips, lovely C25K-ers? Is this just too soon to be trying intervals?