If you don't need the waveform and just want the measurements, then you could just tell the scope to do it and return those values. You don't mention which model of scope you're using but the Tek scopes I use have these measurement functions. Look for a VI called something like Conf Meas. It's a lot faster to return a couple of scalars than an entire waveform. If you need the entire waveform anyway, you can use the function Extract Single Tone Information. This is on the Analyze>Waveform Measurements palette and is not available in the base version of LabVIEW. This function uses a waveform datatype as input and you're probably getting a 1D array from the scope, use the Build Waveform function to and wire the 1D array to the Y input and your scope's sample time to the dt input.