[MarcinK]

I can't speak to comparing other WebDAV syncs to Omni Cloud (which I think is WebDAV too) as I used to sync directly.

If you are looking at increasing speed of your sync, than removing all unnecessary 'attachments' works wonders. I do a lot of clipping of e-mails and webpages into OmnioFocus. The problem there is that all graphical content gets saved as attachments and significantly grows your OmniFocus database. I've cut my db down to 1/4 of its original size by removing all unwanted attachments.

In the Window menu there is an Attachment List, which makes removing attachments that much easier. Also, when I create new actions from e-mails, I'll explicitly select the portion of the e-mail that is of interest to me - this limits what gets clipped to what you selected.