Which is the faster, 830 or 1030+

My advise would be to read this review:

https://www.dcrainmaker.com/2020/06/garmin-edge-1030-plus-in-depth-review.html

"Now the calculation is something that Garmin says they’ve significantly improved here, via increasing the processor hardware. Specifically they said it should be in line with the Edge 830 now and significantly faster than the original Edge 1030. It does seem that way in some places, but not others – notably, not in calculating routes though for me, which still takes a long-ass time (like, many minutes)."

The speeds should be close between the 830 and the 1030.

It would mostly be an issue with route recalculation (which would happen when you went off course).

All the units calculate the route/turns when you load the route (that's what the "Calculating..." is doing).

The bigger screen is easier for navigation and the battery life is longer.

Beyond that, the two are very close in functionality.