Hi Oli, go for the 5'4 as you will outgrow the 5'8" quickly if you already have some background and experience. My advice currently to most people - buy a HAR 2000/300 for the first sessions, then add a 1500/250 wing set as your allrounder/stronger wind setup - one foil is great, but sooner or later you'll need 2 anyway and the 1500/2000 is a great combo, this is what I am using all the time (mainly 1500), previously riding the 1750 a lot..