What should my speed be when I test on the web?

I see a lot of I pay for x but I get Y threads, but no answers. I am on a 600 plan but when I test with https://speedtest.xfinity.com its always in the 200's, sometimes it drops to 100's but typically around 250  - 280. Since I upgraded a year ago I don't think I have seen it over 300.  It does not change even if I connect directly to the modem without a router.

My modem is an Arris T25. Signal seems good. Downstream SNR around 38, Downstream power around 0, hardly any uncorrectables. No disconnects.

I tried every troubleshooting I can find. 

I tried chatting I got a kid that was following a script. After I told him that I always use a wired connection he asked me if my laptop has a good wifi signal "right now". Off course he told me to call Arris.

Before I start my usual, call the 800 number and hung-up when I hear an Indian  accent (from my experience Indians are not allowed to deviate from the script) until I get someone in this country is there anything else I can do to get the speed I should be getting?