The pesky mortgage

As we enter a new phase in our lives, we have decided to start trying to pay off the mortgage in as little time as possible.  I've played about with the figures many, many times (bordering on the obsessional) and have come up with a rough plan to have an overall goal of ten years - 01/07/2022.  The overpayments seem reasonable for this goal (extra £425 per month) and we could manage even with the extra cost of childcare.  But once you start playing with the figures...

So I started wondering if we could do it quicker, perhaps have my 40th birthday as a target which would take it down to 7 years and 6 months.  This gives us an overpayment of £750 per month which would be incredibly challenging and would mean looking for savings in just about every area we spend on.  But if you are going to take on a challenge then you might as well go for it, eh?