In reply to bentley's biceps:
There seems to be a lot of disdain for poles (see 'cheating sticks') in the UK but here on the continent they're very common. I'd never used them but took the plunge a couple of months back in a local mini-ultra - 55km but with 3km of vertical.
They certainly helped and weren't really an encumberance - there had been a huge storm the day before and rivers were in full flow making the crossings difficult - so they were handy for balance. I found them useful in getting a rhythm on the uphills as well.
Best thing is to try. I plumped for some very light collapsible ones - bit of an indulgence but so far so good.
http://eu.blackdiamondequipment.com/en/trekking-poles/distance-carbon-z-pol...
As for sizing - you can get some that adjust, but they're obviously a bit heavier. I'm 5'8 so can't really help you, but if you click on the BD size chart on the link above they recommend a pole length of 130cm for your height. There are other techniques for measuring the height you need - I used this one:
"The second method (requires help from someone) is to imagine that you are holding a pole with your elbow at 90 degrees angle and measure the distance from the ground to the top of your hand. Basically, your elbow should be at a 90 degree angle when you are holding the grip of a pole with the tip placed on the ground. It can be useful to factor in what shoes you are normally wearing when fine tuning what height to choose. For example you may want to round up rather than down if you frequently run in Hokas with high soles and you find yourself between two pole sizes. If you expect to primarily be using your poles when climbing uphill you may want to size down if you’re between sizes."