It's worth giving some consideration to some track racing this summer. You're in good form, injury free and have really solid endurance. You're in an ideal spot at this time of the year. Endurance / threshold we can de-emphasise a little and just maintain it whilst adding in faster work. As you move down to do some 5ks we'll be doing some more 3k and 1500m pace stuff anyway and I think the different training and fresh test of track racing would be good for you long term.
You're mullering all the workouts anyway and I think some new tests are in order - the body can get too used to one 'type' of training and sometimes needs a shock or two to continue the improvement. It's always best to go into these things in good form rather than being forced into it by poor form.
As for the track 10k - rather you than me, but we can fit it in easily enough!!
RunShonaRun - sorry if I wasn't clear, I think it better to start running after you've lost some weight, rather than run to lose weight. As you say running is a more efficient method of weight loss for losing weight, but carries significant risk of injury for the overweight. You can bike and walk for a lot longer for the same level of fitness and do so without risking impact injuries. It's not as efficient time-wise but less risky so that's why I recommended it.
My advice would be to walk and bike for 2 months until you've got your diet and weight under control. Running can wait, the focus should be on developing good eating and exercise habits. A stationary bike would be the safest method and allows the volume to be more limited by willpower than threat of injury.