Not an easy question to answer, because financial settlements on divorce will understandably look on the whole picture and not just one particular asset, although one must admit that the former marital home
( FMH ) nearly always features prominently !
So perhaps I can make a few comments of a general nature.
Where there are dependent children involved, as in your case, the Court will put their interests first , as indeed they are required to do by law, and in particular their need for a home. In your case that need is stronger because your kids are. or soon will be, in the middle of O and A levels, so you do not want any interruption to their education.
There is a very good chance that you would be allowed to continue to live in the FMH while the children are still dependent, and the issue of a sale usually arises only when the children reach their majority. In most cases, of course, this arrangement favours the wife, but there is no reason why it can't work both ways.
It was not clear to me whether you are talking about an immediate sale, or whether the sale is to be postponed until the youngest child is 18.
Where the wife is the parent with care, splits of 70/30 in the wife's favour are not uncommon but there may be a reason for this ; namely that the wife is usually, though not invariably, the lower earner and therefore needs more cash to compensate for her lower mortgage capability. But in your case your wife has a new home, so her housing needs are met, albeit for the wrong reasons from your point of view.
It may be that the Calculator has 'figured out ' that you would be perfectly capable of buying yourself a new property with a 50% split once the kids are off your hands, After a long marriage a 50/50 split would be normal unless there was a good reason for departing from it. I certainly don't think you're likely to get less than 50% and I don't think your solicitor is wrong to talk about 60/40, although I think 65/ 35 is on the optimistic side . Really it depends what view the Court takes about your housing prospects. I personally don't think the calculator came down from Mount Sinai in a flash of green smoke, and I tend to treat it with caution.
The other issue is costs, and regular readers of this website are only too aware of the problems this can cause. The more you spent on lawyers, the less there is for you and your wife. If you are still on speaking terms, mediation
is worth considering. You have to balance the settlement you might get against the costs of achieving it. It is perfectly proper to ask your solicitor for an estimate.