Hi Charlie,
You have posed an unanswerable question. Let me explain why. There are many many variables and how they are accounted for is different between the two.
The alcohol content of your beer will depend solely one the starting and finishing gravities. BUT....
The starting gravity will depend on your losses and your mash efficiency. If you really want to get niggly it also depends on your malt supplier as their may be subtle differences in yield. No-one can tell you what your mash efficiency or losses will be because it is specific to your equipment, your technique and how on your game you are. Beersmith does a pretty good job of ball parking this and can be fine tuned a bit with the total efficiency. This number in itself is not static and requires adjustment depending on the recipe.
Generally lower gravity beers are more efficient in the mash process mostly due to sparge efficiency. Your grain crush will also significantly change your yield. You should also consider that hops suck up wort and need to be accounted for in the final volume going into the fermentor.
I estimate though experience that I need to use 68% efficiency in Beersmith for high gravity beers and around 70% for medium 1.060-1.070ish and 72% for stuff around 1.050. A big double IPA with lots of hops is likely to have a dismal efficiency of 65% or possibly even less. The only way to figure this out is to brew on your system and meticulously measure everything. There are no shortcuts.
Lastly, even when it is in the fermentor there is still quite a lot of variability in the attenuation of the yeast. If you go to White Labs site and look at the profiles you will see they don't give a single number but quite a broad range. Beersmith does a pretty good job of estimating attenuation (which is also related to the grain bill, mash temperature and oxygen content as well as the specific yeast, viability and pitch rates) but it is important to understand these numbers are not set in stone.
I have used the More Beer to compare with Beersmith on the same recipe and they come out slightly different because they treat all the above variables differently. Which one is correct? You have to brew the beer to find out! I think you can be more accurate in Beersmith as there is more fine tuning available to you, but you have to have the right numbers going in to get the right numbers coming out. The last batch of beer I hit my OG exactly and was within 0.08gal of the volume. It has taken me 9 months of fine tuning to get the numbers to work out.
So the only way for you to answer your question is for you to brew more and take lots of measurements
