Hi pvpalval,
I would suggest to go-way-round.
You can monitor the response time of your service using other KPI's (Like webservice avg response Time etc).
Regarding threads, you can keep a check on the state of those threads whether they are in Blocked state, Waiting state etc. Morever you can keep a check on the thread count.
because threads are meant for your connection and smooth processing of the application. What you are getting as Webservice - response time will be more sensible than thread response time as one thread will be linked to many application components.
Hope it helps.
Regards,
Vaibhav