I'd spell it Zachary and Zach. But I totally empathsise with a lifetime of having your name spelt incorrectly... very few people get my name right... but it doesn't bother me that much... only when family get it wrong too!!! No doubt all my kids will have theirs spelt wrong too... but it won't worry me overly... many people are actually dyslexic and/or simply can't spell... it's not intentional so i don't take offence.