Should I accept this GAR buyout offer?

OK so I know that I need to get an IFA to offer formal advice on this, but wanted to ask this question here as I usually get alot of interesting feedback when I do.

I'm 58, married, and retired from my main occupation. I have two personal pension plans, taken out in the 1980s, fully paid up and offering guaranteed annuity rates of 8% (for single life, no guarantees, no annual uplift). One of the plans matures in 2 years' time, and has offered a buy-out of the GAR. It "currently expects" the buyout to be 170% of the current fund value, but they will need to recalculate immediately before implementing the scheme (in December), and can only guarantee a minimum buyout of 153% of the fund value. The usual option of a 25% tax-free lump sum applies regardless of whether I accept the buy-out proposal. The current fund value is £77,100. The buyout offer is £131,000 at the "expected" level of 170%, or £118,000 at the minimum guaranteed level of 1.53%.

So now I need to decide:
(a) should I accept the buyout offer, and
(b) should I take the 25% tax-free lump sum.

Obviously this largely depends on my circumstances, which are:
- Currently retired and spending a net £16k per annum
- Married, no kids
- Homeowner
- No mortgage or debt
- Wife who has rental income from a flat, covering all of her individual expenses (I pay all of the bills and shared expenses)
- One other GAR pension, currently valued at £92k. Maturity date is 2035 (when I'll be 75), at which point it will have a GAR of 15%. If converted to an annuity earlier (at age 60) it would have a GAR of 7.99%
- c.£205k in a SIPP
- other savings of c.£315k, mostly in ISAs
- currently generating £3-5k in income from occasional part-time work (e.g. extras work, focus groups, IT support).

While taking the 8% GAR initially seemed like a no-brainer, I have calculated that if I have other options for generating my required income for the next 20 years (e.g. drawdown on my savings and SIPP), then maybe accepting the GAR buyout and investing the TFLS in ISAs would be a better option for me, for the following reasons:

1. My wife would inherit the TFLS if I get hit by a bus, which wouldn't be the case if I left it in the pension fund
2. The lower rate of annuity from what's left in the fund would leave a little more of my personal allowance to be used to draw down from the SIPP
3. Any future income drawdowns from the reinvested TFLS would be tax-free (if invested in ISAs).

I've calculated that if I can get an average 3% tax-free return from the TFLS (e.g. in a S&S ISA), plus a 4.2% annuity on the remainder from age 60, while being able to survive on drawdown/annuities from my other retirement pots for the next 20 years, the net long-term return from accepting the buyout would never be bettered by the perpetual 8% return if I decline the buyout offer. And of course if I get hit by a bus in the next few years then that option wins hands-down (for my wife, at least).

So there are probably dozens of other considerations that I have missed. I was wondering if anyone could highlight any of the more important ones?