"Up to 300Mbps" is that accurate?

I've been a customer of Comcast for many years (not by choice) and whenever I had service that advertised a speed it was usually accurate within 10%.

This isn't my first time around the block with testing my internet connection, I did it wired directly to the modem using the tools provided by Cox (not the random speedtest.net location) and I am getting between 140-195Mbps. Granted this is not a horrible speed, but it is between 45-65% of what I am paying for. Believe it or not, my upload speeds are spot on. Based on this I should be on the tier below saving an additional $20/month. Or would I suffer from the same ratios on my speeds?

I could do some additional trouble shooting , like taking my modem downstairs to where the cable comes in the house and unplugging everything, but I really don't want to go through the hassle if this is the best it is going to be.