you can have a difference of as many points as you like. then the strategy is called strangle but the functionality remains the same. if you sell 3700 call and 3200 put then you are playing for a wider range and hence will receive a lower premium. a 3400 put and 3500 call will narrow the range but you'll receive a higher premium.
It is only my humble opinion that strangles are suitable when a range formation is expected, however these times do not indicate range-bound action. It appears as though this strangle has little chance of being profitable. One could be very well wrong. What counter measures do you suggest if this strangle went kaput.
Additionally, what strategy is suitable when we expect the market to be trending (at least volatile). Am not too inclined towards bull call spreads or sorts, but more like a non-directional one... please reply at your convinience.