Go with Enstella OST to PST Recovery Software for export OST to PST outlook 2016. You can see their data before the conversion process and convert oversized OST data in PST file formats with the split option. It gives you a free demo version but only converts 25 items of the very folder then you can convert all items of every folder, Now download this premium version on the official website.

Know More - https://www.enstella.com/ost-to-pst-recovery.html