It"s funny how often I watch this programme, and apply the maths to it, screaming at the tv that surely you have to go one way or other, based on what I perceive to be appropriate odds.
Your example of £1k and £5k with a £2.5k offer is realistic, and I would also take the gamble in that spot for the reasons you state...... however with exactly the same odds in play, would you take the very same gamble if the boxes were £1 and £10k, with an offer of £4k (gamble £3,999 for an additional of £6k with odds of 1:1 very much in your favour). Or how about £1 and £100k, with an offer of £35k.
The value of the money, and it"s potential impact on your life status, has a huge impact on the size of your testicles at the time of recognising that the odds of the gamble are in your favour. Amazing how the favourability of identical odds can shift dependant on the values at stake.