Up to now, most of my Sonar work has been using softsynths or plugging instruments directly into the audio card.  I haven't done much work with microphones.  I now have a few mics that that I'll be using and this morning I was doing some A-B recording to hear the differences between them (keeping the EQ flatlined).  That gave me a good idea of the mics' strength and weaknesses that can perceive with my ear.  However, if possible, I'd like to have a better idea as to how well they're picking up the extreme ranges of each mic's audio frequency response. 
 
Is there some tool in Sonar that does something like that?  I wasn't able to find one, but since I'm pretty ignorant to audio processing, it might be right in front of me and I don't know it.
 
If there are not any, are there any plugins that might do that?  Also, I use Sound Forge, but I wasn't able to find anything in SF that did what I was looking for.  (Again, it may be right there, and I just don't know it!)
 
Thanks in advance! - Jeff

To do that you need to generate a sound in the extreme ranges for the mic to pick up.
 
Audacity is a free basic audio editor. It can create sound files with a sine wave at a frequency you can specify - either as a single tone, or a continuous sweep. Record those with your microphone into Sonar and you can compare the level as it sweeps up (or down) into the extreme 20Hz or 20,000Hz ranges.
 
Sounds easy.
 
But now you need a loudspeaker that can turn Audacity's 20Hz - 20,000Hz sweeps into sound waves, linearly.
 
Not only that, you need a sound-dead room to prevent sounds bouncing back and reinforcing or canceling the direct signal at the mic (Anechoic chamber).
 
This is what audio equipment manufacturers have to test their gear.
All a bit beyond us mere mortals, I'm afraid.

Incidentally, unless you are recording symphonic orchestras (or indeed, testing speakers), microphones with a full linear range are of little use.
 
For vocals, it need only be linear over the human vocal range.
 
And even this is not quite true. There are some classic microphones with a good rep because the lift certain frequencies in a pleasing way.
 
And live microphones must prevent feedback, which results in all sorts of compromises.

Objectively measuring a microphone's characteristics is extremely difficult.
 
First, you have the challenge of generating a test tone such as swept sines or white noise that isn't altered by the room you're in. That in itself is nearly impossible outside of an anechoic chamber. And even if you manage that, there is the complexity of a microphone's response, which differs in every possible position relative to the sound source. It's no wonder few outside of microphone manufacturers themselves even attempt it.
 
On top of that, it turns out that such measurements aren't necessary helpful. A flat frequency response may not be desirable for a given application, for instance. Extended frequency response can actually be a problem, as can high sensitivity. About the only thing you can reliably measure is a microphone's self-generated noise, and even that's usually irrelevant.
 
But don't give up! A/B tests are your best tactic. In fact, it's routinely done in studios when trying to determine the best microphone for a particular singer's voice. But the selection is done entirely by ear, and that's an entirely new can o' worms!

Thanks everyone for your great responses!  I learned a lot!

I go back to a simple adage - if it sounds good, it is good.  That's really the only measure.

+1
Just because a mic picks up more highs doesn't mean it's better for cymbals, etc. (sometimes the opposite). When your experience increases you'll be able to judge better when to use which mic. Or how to position it, which makes at least as much of a difference.

When unsure and tracking something/someone, it's not uncommon to do a trial run with multiple mics and then A/B them to see which sounds best in that situation. In the end that will tell you much more than a frequency response graph ever could.

Here's the thing, every microphone has its own distinct character.  That's exactly why they are sought after to begin with.  For example a Neumann U-87 may be perhaps the most sought after vocal microphone of the 50' through the 70's.  Though it is still quite popular now, there are many other brands who have found their way into the ears of producers and engineers.   I think it would benefit you to check out the actual hearing spectrum of the average person.  You find that extremes on both ends are useless for the most part.  So now, you really do come down to the character of a particular brand and microphone.

I might be going slightly off topic here but Microphones seem to be a trial and error thing with me.
When I only owned 4 mic's, I used those 4 microphones to the best of their capability's. then as my microphone collection grew, I began using different microphones for different jobs. When I look back at it, I probably squeezed more out of those first 4 microphones I had than I did with the 16 I have now.
 
Of course there is certain do's and dont's and there is of course grabbing the right tool for the right job but it took a long before I found a microphone that (I felt) fit my vocal range and had a nice sweet spot for where my vocal range is and that Microphone is a Rode NT 1000. Im sure there is better out there but to go back to what I said earlier, sometimes using a microphone to best capability's is the best practice. Not so much being concerned with the science of it, but what it sounds like in different settings.