if you had an afr of 13.5 peak between 7k and 8k rpm on a SC CC car would that be too high to run on track?
Hmmmm thats a very good question, one I am sure that in the fullness of time will be answered by somebody who actually know what they are talking about 
Thats an easy one to answer Ade …
If it blows up it’s too high!!!
I doubt it very much - if it was 14+ I’d start to be worried but you’re probably just not getting the max available power out of it - that’s all.
As long as the ignition timing is ok (ie your using high octane fuel) and the knock sensors are working ok just in case then it should be fine. 13.5 is not ‘lean’ by definition, it’s just less rich than 12.5 IYSWIM.
This takes me right back to Westfield days 
What wideband do you have? Innovate?
yup…^^^^^^^^
At full throttle and boost you should not be above a target 12.5 af.
Also the important thing to remember is what is your ignition timing with those af ratios…