The exeuction speed of DAQmx is definitely faster than the execution speed of Traditional DAQ. However, in your case, you are seeing a slower load time. I believe the reason for this is actually .NET as opposed to DAQmx. When using DAQmx or Traditional DAQ in an API that allows for both, I have never seen a speed difference in loading.
Check this out too:
http://zone.ni.com/devzone/conceptd.nsf/webmain/EE47B125BB9E053686256FBC0014C384?OpenDocument&node=10181_US
Regards,