Thank you for your answer. I have never tried expensive mics but I remember that MS mics can be a good compromise; I pulled some mice recordings with a stereo MS sony ECM 979, which I don't own any more, and I tried a Shure VP 88 with appreciable results.
I've experienced the fact that my Natant x-x omnis may fit perfectly in medium -big halls in order to record a full sound, but may sound terrible in presence of very reflecting situations like a church or my home, in which I "packed" my Steinway D concert grand in a small room. In any case I need time to search for the best position, time which I often don't have in order to get a recording for archive purpose.
A musician's life is often like getting into the hall a couple of hours before the concert and being concerned with rehearsing the program, change suit, have a short rest, go and play. After the concert there are always people to talk to, change back your suite, take the scores and be ready to go to dinner.
The Shure VP 88 or the Rode NT4 ( or the cheap Supberlux E523 or the AudioTechnica models, which I don't know) all have both phantom power or battery option. I have time and space in my luggage and somebody helps me? I bring my littlebox, my Edirol R01HR, xlr cables and set everything fine. We are in video age,then, so if I want to have a video I need also at least to place a cell phone for filming.
I don't have time or have travelled on a plane with a handbaggage? I bring my stereo mic, a violin music stand,plug the battery powered mic into the Edirol and go.
Since the moment my Sony ECM 979 died, I found myself most of the times bringing just my Edirol, place it on the ground or on a chair and press rec. As we usually say that the best camera is the one you have with you, thus taking mostly pics with your phone than with your 1000 bucks Canon you have at home, I ended up thinking that the best recording set is exactly the one I can bring with me.
That's why I'm trying to explore the fastest solution with a certain quality, even accepting compromises. Should the VP88 have a lower price ( and maybe a lower noise floor....) I'd certainly go for it.
Probably the Supberlux E523 id really too cheap and, in the middle, I guess there is only the Rode NT4, but I don't like the recordings I've heard from it.