Might as well as my bit......
I converted my NZ/OZ CPL (with ATPL theory) to the JAR's 3 years ago. It took me 9 months, mainly due to the first school I enrolled at going tits up, and then having to re-enroll elsewhere.
Distance learning was the way to go for me, I was able work and study. The toughest part I found was the sheer volume of work, the technical aspects were not particularly difficult, there is just so much of it.
Took the exams in 2 blocks of 7, passed them all with an average mark of 88%.
I used oxford aviations' course..a bit pricier but the results were worth it.
What ever you decide to do..make sure you do the research