The first kilometre could have been faster -- the group of us were all conserving, but conserving a bit too much. After that, we were all pretty consistent. But I couldn't stay with the group after the 5th repeat -- it was all I could do to knock off the 4:20's that I did.
The good news, though, was that my hips weren't sore, as they had been when we first started doing speed work. My back was a tiny bit sore that night, but nothing serious. So it is possible that all this speed work is having the positive effect for which we've been looking!