In this particular case, I'm using the "probabilistic" method. In this particular case, each long option is about at the 15% probability ITM strike and each short option is about at the 70% probability out of the money strike. This relieves me of having to look at each individual option's delta and tweaking this and that to get a fairly delta neutral setup.
The additional criteria I'm using for this particular setup is that I attempt to get at least 1/3rd the width of spread in credit. Since the wings are four strikes wide, I'm looking to get at least 1/3rd of the width or about 1.33 in credit for putting it on.
These are the metrics for the setup:
Probability of Profit: 52%
Max Profit: $140/contract
Max Loss/Buying Power Effect: $260/contract
Notes: Unfortunately, with this low in the broad market, twisting premium out of index ETF's is difficult here (even though IWM is the "best of the bunch") ... . This is why you always go small, dispersing risk across a large number of setups put on at different times in different expiries and at different price points.