Download Accelerator uses four threads while HTTrack has a selection up to 32
threads.  That means that your Download Accelerator is eight times slower at
maximum selected settings, so I would not use it.  

I was also able to type "50" into the selection line for HTTrack's "Number of
connections" setting, though I don't know if HTTrack would keep that setting. 
Running more than 10 simultaneous threads will probably get you disconnected
from the web server, if the webmaster did his/her job, or, if they didn't, may
even crash the server that you are trying to mirror.  

I often run a mirror over only two to four threads to make sure that I don't
"hog" the server too much.  Generally, I don't think it makes much difference
whether one uses four threads or 40, since the connection is running close to
maximum at four threads, anyway.