Bang for buck in Northeast: U-value most important factor?

[spup345]

I just ran a bunch of simulations in ResFen5 for NY, slab on grade, gas furnace, typical window layout.

You can adjust for U-value, SHGC, and Air leakage to determine the annual energy cost for the house.

Since the 30% tax credit is too good to ignore, I started with a base case of (all windows, same config):
U=.3
SHGC=.3
Air Leak=.3
Annual cost $1197

I then adjusted the values, holding the other 2 constant at .3, and found:
-U-factor of .15 will save you 6%/year
-SHGC of .45 will save you 1.7%/year
-SHGC of .45 for SOUTH windows ONLY will save you 1.2%/year
-Air leakage of .15 will save you .5%/year
-SHGC of .15 will LOSE you 2%/year

So, according to the software, it looks like if you are looking to maximize energy savings in $$, the only number you really need to care a lot about is U-factor.

I ran these simulations because I was concerned that the low U-factor tends to require a low SHGC as well, but that's really the only way to maximize your savings since a higher SHGC along with a higher U-factor, would not be "bang for buck".

I am replacing south-facing windows so I wanted a high SHGC and low U, but after running these sims, I now realize that:
-Going higher than .3 on SHGC is not worth it because the $$ you save with a high SHGC, you lose overall due to missing the tax credit as well as requiring a higher U-factor

So, my ideal window, it would seem, would be:
-As low a U-factor as possible
-A .3 SHGC to get the tax credit as well as maximize SHGC
-As low air leakage as possible
-As high Visible Transmittance as possible

Does this all make sense to the "pro's" out there? Because this would be an easy template for me to compare during my window shopping.