I started out in Variax-land with a 300 and now have 2 JTV's, a 59 & a 69S, but I did have some issues with the 300. I always used 0.009's on my strat with occasional breakage towards the end of the strings useful life, but with my 300 set up with 0.009's, I would get only a couple of shows played, and would have a string break -- usually the B string, if I recall right... Don't know if it was saddle related. ANYWAY, I changed to 10's and the problem stopped. I had to get used to the slightly heavier gauge, but now that's all I use. I do hand vibrato and note stretches like everyone does, and (knock wood) haven't popped a string on my 59 or 69S. I don't really use the whammy on my 69S or on my strat, so don't get much breakage related to that. Now using 10's is just out of habit. My strings start going dead on me before I break any, and I change them more for that reason. 11's seem a bit stiff to me, but it's usually the lightest string you can get for acoustics, so my hands take more of a beating when I play my acoustics or my acoustic/electric... My acoustic 12-string really makes my fingers sting if I play it for any length of time....
Thanks Dave. I have a feeling the Variax chokes the strings a slightly more than on other guitars. It might be my piezos being old or something, but it does have a bit of an edge on the saddles and piezo, which is where I think it's choking the strings, so you basically might have a sharp angle that the string bends and sits on, both maybe weakining the string a bit and breaking it more than normal saddles.
I did lower the action a bit because I think the saddles were angled a bit up so that might be doing some choking too, but I don't want it too low or else it'll start buzzing out on the frets.