The difference is very minute. If you like the look of the grids, get them.

No. The grids are designed to be suspended between the panes of glass without touching either surface. This is designed so as to not scratch the Low-e surface and to negate any conductive losses that might be the result of the thermal bridging of an aluminum grids.

Metal suspended in the glass will raise the U-factor in theory because it does act as somewhat of a thermal conduit and also reduces the volume of argon or other noble gas in the void space. This is in theory and the realized difference is nearly imperceptible.

You will notice a drop in SHGC as grids will cut down on the Solar Gain by reducing the amount of light and solar energy entering the home.

Wow thanks, that clears that up, thanks to everyone on here you have been a tremendous help for us. This is a big expenditure and being able to get quick answers to questions like this really helps.