I think eye-SAY-us would be misheard (in English speaking places) as Isaiah's, which would annoy me if it was my kid. And I think eye-SYE-us isn't a very intuitive pronunciation (again, in English speaking countries), so you'd have to be willing to correct people without getting annoyed. I don't love the sound of either.
Three boys nappin', one mama namenerdin'
To peruse my top 100ish names:
http://www.behindthename.com/pnl/82589To peruse my non-name musings:
http://jodifriesen.blogspot.ca/