Floating floor over uneven timber floor

After lots of planning and preparations I started laying a floating floor - in the hallway, since there is no furniture to move there (which lets me stop and start over with minimum trouble).
Unfortunately, the existing timber floor is very uneven - typically higher at doorways. Each existing floor plank seems to be reasonably flat, but there are differences from one plank to next.
I know that 3mm of 'unevenness' can be tolerated; but what about differences in slope, e.g. where a level surface meets a flat but sloping surface? What is the maximum permissible angle? Any differences in 'lengthwise' and 'across' angles (may determine which way to lay in other rooms)?

I plan to use some filler to smooth out valleys - would 'Builder's Bog' be a good choice?
Rows of nails make sanding 'hills' a difficult proposition - any better suggestions?


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