The max bundle is only worth purchasing if you need the flexibility. Even on the cheapest fare, you can purchase the extra legroom and upfront seats

In the original post you indicated that you could still have 20Kg of luggage on top of the 80Kg allowance ( total 100Kg )

This would cost an extra SGD400 on Jetstar
With Singapore, the excess fee is less, but the included allowance is only 20Kg per person. 60Kg of excess fees at $12.50 is an extra $750

I would say that this would make the excess fees higher on SG by $350 , plus an extra $106 per person extra on the fare making it $562 more expensive