Thanks for the feedback!
Since the battery life of my PW so far hasn't been an issue (I basically need to charge once or twice a month), the longer battery life of the Oasis wouldn't be a huge bonus. And everybody says that the ergonomics of the Oasis is better IF it's without the battery cover, so it looks like the extra battery life definitively won't be a selling point.
Looks like I'll go with the Voyage then. Now I just need to convince myself that I really need a new Kindle to replace my current one that is working perfectly fine
.