As of Alice's game power five boxes have came to the table 41 times in season 4.

£35,000 – 5 - 12.2 % - Won 2 times (out of box)
£50,000 – 13 - 31.7% - Not won in Season 4
£75,000 – 6 - 14.6% - Won 4 times (out of box)
£100,000 – 6 - 14.6% - Won 1 time (out of box)
£250,000 – 11 -26.8% - Won 1 time (out of box)

£50,000 has came to the table the most out of any other power five ammount. But it remains the only power five box win still to be won in Season 4

Interesting!

Nice, I pray that someone wins £50k out of the box!