For your current speakers 140 is far enough - same if you upgrade. Frankly if you need more SPL then get a bigger speaker (three way) rather than overdrive a small one - your little speaker will be mostly distorting when driven hard.
FWIW: If you are looking at really old amps then it may be worth having it checked out and possibly replacing the caps.
FWIW: If you are looking at really old amps then it may be worth having it checked out and possibly replacing the caps.