Many thanks to you all !!
Clearly, there is not a whole lot to choose between them, based on these opinions, which is more or less what I expected. There were 2/12 clearly in favour of the ZI, 5 in clearly favour of the CVs (one suggested I get two), and 5 basically saying it is a toss-up, many pointing out the pros and cons of each camera. Two or three mentioned the difficulty of reading the shutter sppeds on the ZI, a point I had noticed when I looked at one at B&H a year or so ago. One pointed out the (significantly) louder shutter on an older Bessa 2, but it seems the later Bessas are just about the same (as the ZI).
I won't decide for a month or so yet, but I'm seriously considering the Bessa 3a (and maybe a 4a to go with it). I (nearly) always carry spare batteries, and I like having the Av option, which is also available on the M7. I'll only sell this later if I'm entirely happy with whatever I get, or maybe not even then.
Once again, thanks for lots of valuable advice.
Since you already have an M7, why would you want 2 Bessas? Or are you saying that you also want a 3rd body?
If you get a ZI, you may find that you like it better than your M7 & the M7 may be relegated to being your 2nd body.
When you buy a ZI, here are some things you are getting that you do not get on the Bessa:
1. Long rangefinder base for more accurate focusing, the longest effective base line (55.5 mm) of any camera ever made which includes 28 mm frame lines.
2. Short time lag of only 14 milliseconds in manual mode & 20 ms in AE mode. This is very similar to the time lag of your M7. However the Bessa R was tested by Popular Photography with a much longer shutter lag of 100 ms, which is closer to a typical SLR than to a Leica or ZI.
3. The shutter release button has a depth of travel of only 0.9 mm. Compare that with your M7, which has a depth of travel of 2.0 mm. The first 0.6 mm of the ZI's depth of travel is to activate the meter, leaving only 0.3 mm further that the button has to travel to release the shutter. Combined with the short time lag once its shutter is actually activated, the ZI provides immediacy of response that is almost unparalleled. And immediacy after all is at the very heart of rangefinder photography. In addition, there is significantly less force required to depress the shutter release button, which is a benefit when taking hand held pictures at slow shutter speeds while maintaining a steady hand to hold the camera.
4. The metering pattern in the ZI was improved over the one previously used by Cosina in the Bessa series & is more accurate. Moreover, the AE Lock button allows for "permanent" lock (20 secs,) to further assist in metering without having to hold it manually depressed while compsing your picture as is the case with Bessa cameras. I also find the location of the AE Lock button easier to use with my thumb.
You'll also notice that when compared with your M7 that the frameline options offer a range of 28 - 85(90) but without the extra clutter of 75 & 135 framelines as you have on the M7. This makes the 35 & 50 mm settings a joy to use as those are the only frame lines which appear in your view when you use those respective lenses. Another advantage over the M7 is that the ZI is virtually flare free due to differences in design of the rangefinder itself.