I hope these few nuggets about PhantomJS can help your app:

- Use JPG and not PNG (for renderBase64), we tested it and JPG gives a much more better performance, but then again it depends on how crisp you want your output

- (You may already done this either using PhantomJS or using image manipulation) Don't forget you can also scale the image using page.zoomFactor :)

- (Not sure how useful this one is for your case) You can clip the viewport too in PhantomJS

- PhantomJS seems to use a lot of memory (main page of twitter.com may resulted in at least 45MB of memory).

- CasperJS is probably the best wrapper of PhantomJS out there for now if you ever need to do something more complicated