Steve, presumably you are happy with the E-werks by the sounds of things? Ref the Iphone, I'm inclined to agree with Jack that the Sat Nav function for 3GS and beyond, depending on which app you get, circumvents the need to have internet downloads which incurr the costs abroad. In any case, I'm about to put it to the test and will report back.
I'm thinking I'll almost certainly invest in E-Werks regardless of which route I go - the freedom of being untethered from the demands and practicalities of recharging equipment on tour sounds great though I'd agree with comments about paper maps. I wouldn't go without them and sitting down and just looking at them at the outset to anticipate and plan the adventure ahead, is IMO, has always been one of life's more gratifying experiences.