Pace for 25k set too high?

Hi everyone, I started swimming in 2011 and have managed to work up to a few 10k's in 2012 but am looking for the next step up. I was interested in the Mollorca best fest 25k crossing but it looks like you have to keep up a minimum pace of 3.4k in 55mins or you get pulled. My last 10k in Bray lake was WITH a suit (for comparison) and it works out at 3.3k per hour, a pace I may not hold for 25k in the sea. Is this pace normal for these events and are they strict on it?, as they only have 2 boats for 250 swimmers.
Has anyone done this and are there any similar swims 10-25k with no time limit?
Has anyone done this and are there any similar swims 10-25k with no time limit?
Comments
http://xtrmswim.com/cabrera-channel-25km-2/
I'm all set to have a go at this in early April.
Best
Karen