Ok so I took some advice (first time for everything!) and slowed it right down this evening, 8:00 average pace.
My app calls for 70% HR or able to hold a conversation, so I sung all the way round to keep me on track (I owe the people on route a huge apology!). Found the run so much easier from a cardio POV, at no point did I think I was going to die, but my muscles?! OMG!
The programme I am following is to burn fat and boy did it burn! I found it so much harder to go slower but felt it was better for my shape rather than my fitness if that makes sense? With 50lbs to lose I get that the fitness and speed will come once the weight has departed!
A steady 3.8k in 30 mins and I feel it will benefit me more than the 4.34 on Tuesday, weight first, speed later!