Last month a test was conducted by Robert Rozak, President of juicedLink, comparing the preamps from his company's products with a similar offering from Beachtek, with both going right into the Canon 7D. He received so much feedback that he's added a number of devices to the test and is now comparing the signal-to-noise ratio performance of the preamps of a number of devices, the Sound Devices 702, Zoom H4n, Tascam DR-100 MKII, Tascam DR-680, Edirol R44, Beachtek DXA-SLR PRO, and juicedLink Riggy Micro/Assist. Click through to see his results.
Video is no longer available: www.youtube.com/watch?feature=player_embedded&v=KKVeBqhXMvM
The results aren't very surprising if you've used any of these devices before, though the results of any of the recorders would certainly be improved by using a mixer with a good preamp in front of the recorder. The Sound Devices 702 is actually the recorder that I use most often, combined with a Rode NTG-3. Even in difficult situations and without a mixer, I'm able to get stellar results. The juicedLink still seems like a good option as a preamp regardless of the final recorder being used (even if it's a Canon 7D or Canon 60D), but you will find that the more sensitive the microphone, and the closer you can get it to the subject, the better the signal performance should be.
I'm sure some of you will take issue if you own any of these devices and you've been happy so far, but it's always best to do your own testing, as it's certainly possibly that you're getting great results from the equipment you have.