Depends on whether you're prepared to front-load this one. If you are, you could get away with a fast 6.3 miles then relax but accept that your time for the whole thing might be slower than you would have done otherwise.
I like to set off relatively slowly, but my flat marathon time is 3:09 and I'm sort of OK on hills, so I'm hoping that the cut-off won't be an issue for me.
Superglue - I agree with everyone that this is a fab photo. I'm still really disappointed that I couldn't be wading through that water! But I've now entered the Dig Deep Intro Ultra in July - 30 miles in the Peak District. Not as long, but there'll be more hills and navigation involved and I'll still be able to claim to have done an ultra before I turn 40 which was the goal I set myself last year. I'm not overly worried about the navigation since the race is very close to where I grew up, but I'm expecting to add to my time and, possibly, the distance depending on just how lost I get.