So, today I managed to test and compare the dualband-patch antenna in the same 60cm offset dish.
The patch radiator was placed in focus, like where the Octagon LNB was before. I compared, one after the other, the results from the previously shown dualband helix-LNB with the patch-feed and found for both systems similar signal-levels from my uplinked signal. Only a difference of abt 0.5dB for maximum signals with each feed. Measured SWR of the patch in the focal point a bit under 1.3, so that's fine.
(Pictures of patch-feed were taken after the test setup was removed)
73 Ed