Keep cool, just wait and see what happens once you're on your new contract. The device should be just around in the ballpark of that throughput, so just skip what-if's and test the real situation once you can.
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and yes, I'm very interested in the results as well.
I have one on 1000/500 fiber now but I'm not at the site so can't do much testing now. I don't yet have anything else in the network fast enough to run a test.
With OpenWrt, no SQM, it did speedtest 840/450 on the installer's laptop. This was 2x2 ac wifi at a short range.