If it was me I would do 6 15's if they can fit under the window line like you want. My current set up is 6 SA12's and I am able to do 148-149 on 3 minute music runs with no issues. I have seen low 50's on some 30 second runs. I am able to burp around 152 with no issues. But my box was not built for burping it was built for music...
For me I would not tune under 34, no real reason.. I have tried 28, 30, 34, 38 and 42 and I prefer 34 for sure.
Here is a quick video that was taken about a year ago..