Since no one has responded, I will give you my take on your situation.

First, a question.   Is the house comfortable now?  I am guessing that your current windows are plain glass, which would be high solar heat gain control.  The difference is that virtually everything now has low-e coatings and the solar energy that enters your house stays there. Using interior blinds or shades for solar control is less effective with low-e glass.

If you need blinds or shades for solar control in the summer to keep comfortable now, then I would suggest low(er) solar gain control glass unless you can do some exterior shading.

If you mix high SHGC and low SHGC, you MAY have a slight difference in appearance between them....just something to keep in mind and would probably only be noticable if they next to each other).  You do not need tinted glass, although the modern coatings give a very slight mirror effect which increases with solar performance (not usually a factor in residential applications).  Don't think in terms of hard coat or soft coat, but just look at the performance numbers.

Since you live in a mild climate, you will get less benefit from argon and super-duper insulated frames than someone in northern Minnesota.  There is a benefit to be sure, but the payback will be longer.  It seems that argon is almost standard today in good quality windows, so it may be moot.

I would let your budget and taste guide you as I think any high quality window from a reputable manufacturer will serve you well. 

What you DO want is a really good installation to keep air and water out.  I think $20 spent on minimizing air infiltration and good water control is a better value than a more expensive window.  Your installer is a bigger variable than the window manufacturer.

Good luck,
Bruce

You should find this website helpful for comparing different solutions:

http://www.efficientwindows.org/selection.cfm

Efficient Windows is a good starting place for information, specifically on glazing sustems. You also need to go to http://www.energystar.gov. It is a governement site that has listed tested and certified windows that meet the specific requirements of your location. You need window that meet the minimums for your Energy Start zone. That said, there are several factors to pay attention to:

SHGC the lower the better for cooling loads. If you make it too low for your location, you will force the heating systeme to work harder and spend more energy to heat the home. Also, you must pay close attention to the visible light or Vt factor. To get to lower SHHGC, some manufacturers darken the glass. That will mean you will have to probably add interior lighting during the day in darker rooms and that can offset the energy savings. I would sy that best solution for you would be something that gives you less than .40 SHGC and Vt of more that 60% such as Guardian RLE glass. Excellant properties for energy conservation and Vt.

Gas fill can enhance the U-value fo the IG, but there is still a lot of controversy over how long the gass will remain in the cavity. If you select a IG with a U-value of .35, that will probably be an optimum for North Carolinas and you can achieve this without gas.

If you live anywhere near the coast, I would seriously consider impact rate glass, or at a minimum of laminated glass with a .060 PVB innerlayer. This would not be impact "rated" but would offere some added protection against breakage. It also makes you window more secure against break-in and will make the window quieter.

For more information, read this: Best Vinyl Windows