Yes, that speedtest site is pretty reliable. The problem with many sites is they have limited bandwidth available so if they're busy then the readings will appear low.

Anyway, looks like your speed is pretty good now

With regard to the errors, they're only a problem if they give you a problem. You already have a filtered faceplate and say that the test socket is no better. That points to a line noise problem arising in your BT line. With a sync as high as you have some errors are inevitable. If you think they are a little too high or are giving problems then you can always up your noise margin a little (use Mognuts) which will lower your speed slightly but may reduce the errors.