There is software to convert your designs in your library to the new format you might be using. In my opinion that might be your best bet. I used to use Embird when I did that but my sub ran out. It is a good thing to have.

If you already are using pes format, then you will be fine with the 780D. If I am correct, that machine will use the usb stick or plug into your computer either way you wish.

The 780 will use both 4x4 or 5x7 design formats.

I believe the 780 also uses 90 weight bobbin thread. Most other Brother machines use 60 weight. Some of them can be really finicky regarding the bobbin thread.

If I need to convert designs I use Buzz Tools.

I love my Babylock Ellegante
Bernina is too expensive for embroidery.
Pfaff has jammy bobbins.
Imagine Janome does good--saw some impeccable embrpideries from Janomes.