It's not easy to answer. You should always use your sub advantages over enemy sub disadvantages
Playing againstAI is also completly different than vs human. AI is like not very smart cheater
For example:
Tracking AI sub is usually very easy but tracking player sub is not.
For me comparisoning noise levels is common mistake. It doesn't really matter because as you wrote in first post, you knew somewhere was Sturgeon - so you decreased speed to 3 kts. What was Sturgeon speed? 10 kts?
I mean: if someone make ambush for transiting sub, almost always can be very quiet.
Problem is when you have to run fast (you are part of screen of convoy moving 15 kts) and on your route are submarines at very low speed - almost undetectable.
So, your noise level is not crucial, but yout maximum tactical speed and firepower (good torpedoes or wide weapon variety)
When you launch torpedoes on enemy direction he have to evade and he cannot track you like before. So it's good idea. After this you should increase speed (enemy probably is deaf at this moment*) and change course: move away from enemy torpedoes "interception point"
* high tactical speed allows to run away while tracking enemy
Check UNSI REFERENCE in game - there are informations about sensors