If you are using a TurboTax CD/download version of the software, you can create more than one return with the software (and just not file them all), therefore you could create returns to see the comparison of filing separate versus joint -- create one return as joint and then two others for each of the married filing separate returns.
The FAQ below is worded for a different scenario (filing federal joint and states separate), but the concepts are the same for creating joint and separate returns in TurboTax.
https://ttlc.intuit.com/replies/3301995