I disagree with the last comments.. Your typical external print servers are normally FASTER..
This is in part due to its standalone processing of print jobs..
If you get an internal card to print from then it will rely more on the unit for processing power..
Now granted you can get some pretty cheesy print servers with low memory and job spooling capabilties, so choose a higher end unit..
If as you stated "speed is your only concern", then definetly without question go with an external print server.
Now all this is with the understanding that when you say "internal print server", you mean one that you install on you computer.
If you mean internal/native to the printer or built in then they are usually fine, but still rely on a printer/its memory/its boards to perform work.. Food for thought..
Good Luck