I've been running a V2 / X2 combo for a while now (2 winters plus), both on 183 rotors. The V2 on the front is a superb brake – powerful and well modulated for single digit braking. The X2 has plenty of modulation, but is lacking in outright power. It does make a good two finger brake (where you can apply that bit more more oomph), but just isn't up to the job as a one finger brake (IME). I've just bought another V2 caliper and will be swapping out the X2 soon.
You might be interested to know that Hope have completely redesigned the V2 caliper (and apparently told nobody about it). It is a much smaller unit now and is very similar to the X2, but retains the same pistons i.e. it has the same power as before, but much less weight (and less heat sink capacity). Honestly, I can't see why anyone would buy an M4 at all now. M4's are only marginally more powerful then X2s, but are quite a bit heavier – the new V2 simply kicks them into touch.
HTH