While there are limits in how many mg/ml different steroids can be mixed at (they won't fully disolve without going through extra ordinary means in what chems you use to mix to disolve, if memory serves 250mg/ml for test cyp isn't out of the standard range. I'm not a reg steroid user anymore as I'm in my mid 40's and my diet is far from optimal for someone doing cycles I think the last time I ran cyp it was 200mg/ml or possibly 250mg/ml.
BTW this stuff can be googled, there are a lot of guys with decades of experience who contribute their knowledge and experience on the net. The advantage of doing research on the net is you can get 2nd and 3rd and 33rd opinions fairly quickly to see if what your researching is contraversial or not. Plus the mod on this forum really seems to know his stuff which is really great because most 'drug' boards/users consider steroids to be like not drugs and IMO the vast majority of steroid users are very predjuiced against 'street drugs' (and even a lot of other medications, that may be prescribed by a psychiatrist for example.