In reply to Levy_danny:
> thanks for all the help everyone, I'm going to try the calf sleeves for longer distances
I've seen this mentioned a lot, and ultimately so long as you're happy with your choice it doesn't really matter but I think again there's limited evidence that they make that much difference.
I've been running ultras since 2013 and have never worn them. I used to get cramps in the later stages of longer, hillier (eg. harder) races but now it's not an issue. Years back I used to get cramp in a 85km/4500m race whereas this summer I ran 170km/10,000m with no cramp whatsoever. The only difference is that I'm now fitter and more used to the distance, and my race strategy was better and I kept my pacing under control.
I'm pretty sure it's simply down to over-fatiguing your muscles - you're simply not trained enough to run at the intensity and duration that you are - so either train more or run slower. Get that fundamental nailed and then start looking for marginal gains.
Good luck at the weekend!