I finally ended up buying both the Rode SVM and the Azden SMX-10, and spent most of the weekend testing them.
The Rode SVM is quite simply too large for me on the HDC-TM700. When placed on the cold shoe it would tip over the camera (I have a quick release plate under the camera for my tripod). Notably the QR plate has a flat bottom, but the Rode was so front and top heavy it was unstable. My wife said she wouldn't use it, it was uncomfortably balanced in her hands. What with the size concerns, and then with the deadcat muff showing in the field of view at anything wider than optical 2x zoom, it was a fairly quick conclusion I wouldn't be keeping the Rode SVM.
Having said that, I did try many sound quality, and signal to noise tests comparing the Rode SVM, the Azden SMX-10, and the built in microphone set to the Zoom or Stereo settings.
The built in mic does pick up some fan noise, it's annoying, and clearly audible in a quiet room. It's totally obvious when recording in a silent room and playing back the audio at maximum volume on the camera itself. However, having said that, when fixing the audio level (set to -3, and AGC off) I ran several tests where I had a CD playing at a loud volume level and other parts of the test where the room was silent. Using this I could use Adobe Soundbooth or Premiere to adjust the audio peaks up to 0db, and find out what the noise floor was. I was shocked to find that in this test, the noise level of the two external mics was the same as the built in mic!!!!
This is a revelation. Ultimately I think it means that the audio circuits of the camera are so poor that it doesn't matter what kind of mic you use, you'll get noise to a certain level because of the camera. Spending lots more on the microphone isn't going to do much good if you plan on recording the audio through the camera.
When I was done with my testing, I found the Signal to Noise ratio of all three microphones (Rode, Azden, Built In) were quite similar. However, the "color" of the noise was quite different. The built in had a mechanical fan noise to it, the Rode was slightly quieter (perhaps 2-3db less noise) but had a hiss and a hum. The Azden was noiser than the Rode (almost idential to the built in in pure signal strength) but the noise was entirely hiss only, a much "whiter" noise.
I was EASILY able to remove all of the hiss/hum/fan noises from all three from within Soundbooth - what an amazing tool.
I also tested how nice the audio sounded, with both male and female voice (thanks to my wife for being patient), and also heavy metal music (Joe Satriani) and female vocalist (Lisa Stansfield). The initial tests showed little difference in the audio quality with any of the mics. Honestly, if I could tell any difference, the Rode lost, I couldn't easily distinguish the other two.
Finally I tested the mics with a 20Hz-20kHz sine wave frequency test. The biggest surprise here was the Azden picked up the lowest frequencies with the strongest signal. This is entirely contrary to the "specs" which just goes to show how bogus specs are. The Rode claims 40Hz to 20kHz, the Azden only 100Hz to 17kHz. However, as neither of them state the dB drop off for these ranges they are meaningless. My tests showed the Azden picking up signals at 55Hz through around 14.5Khz, and the Rode 68Hz through around 17kHz, the built in mic fared very well, from 65Hz to around 17.5kHz.
At this point I gave up on the Rode. The size was too much, the audio no better in any test I threw at it.
I kept going with the Azden a bit longer, heck, it only cost $65, and I really really wanted it to work. On my prior camera an external mic was hugely better than the built in, 12dB more focused, and 10dB less noise, so I had a strong belief that the external mic must be better than an internal - it's what everyone says too, so I was seeking positive reinforcement of this.
My final test was wind noise. I walked around with the built in mic, and with the Azden SMX-10 with the wind muff outside, it was quite windy so I picked up several gusts, both head on, and sideways. The internal mic was WAY WAY better.
Anyway, to say I'm surprised would be an understatement. I've sent both mics back, and I guess I'll just be using the camera on it's own. The fan noise is "bad" but when I compared it to my previous camera, it's no worse than the tape motor noise that my prior camera, with external mic, captured. Although to be honest, although the SN ratio may be similar, the color of the fan noise is worse. But having found Soundbooth to very successfully eliminate the noise pretty much solves the problem.
Clearly the built in mic (in Zoom or Stereo mode) is actually quite good.