Tough question Moose. I'm curious what others will have to say. I get a bit confused by inflation/real returns sometimes. I'll offer these thoughts/numbers:
You have 25 years of compounding. In 25 years that 37,320 could be worth:
5% return = 126,379
6% return = 160,173
7% return = 202,552
8% return = 255,585
9% return = 321,813
Those are not adjusted for inflation. You mention a 5% real return would not reach the $316,500, so I guess you're looking at a 7-8% return?
Other variable worth considering:
1) Taxes. Lump sum will not net $37,320 unless it can be rolled into an IRA.
2) Life expectancy. Your wife would have to live 30 years (60-90) to achieve the benefit matched by the 4% SWR. If she doesn't, what are you left with. In the lump sum scenario you or your kids would still have the principal amount invested.
3) Pension Funding. It's backed by a very strong state, but I wouldn't want to depend on a government body to fund my retirement. I would take a pension if I had one, but I would do everything I could to gain control of the funds.
I think the key here is waiting for the annuity leaves a lot up to chance, particularly your wife's life expectancy. Taking the lump sum puts it within your control.
The use of the 4% SWR in your analysis is interesting. I guess I understand why since it's an often used metric, but does it really make sense here? It provides an 80% probability that you wouldn't run out of money. But in a lot of those 80 out of 100 scenarios you end up with an incredible sum at the end of the 30 years.
Lastly, I wouldn't factor your wife's possible return to work into this equation. From prior posts you've mentioned freelance work before reaching a 4% SWR. Unless she is pretty sure she'll go back, leave that out of the mix.