Just to throw in my 2 cents.. I have used Rithmic for years and while there are some things I cannot stand about them, lagging and what you are describing isn't one of them. I stare at the DOM all day and I cannot remember the last time it got hung up. ? Granted I only look at ES and NQ though.
If you do need to use that feed, just know that is not normal (At least on the 2 markets listed above).