The line upgrade has worked flawlessly. DNS system has been updated too - as I could not keep my old IP-Address. Seems the Automated systems at Nefkom are not able to perform certain changes by keeping some of the old data.
Anyway - a speed test shows that we have a constant Downstream of 12MBit and 1mBit upstream - which seem to work correctly. So - outside accesses to Stargate should be even faster now.