We are building an ICF home w/ R49 attic in zone4 of lake tahoe (think cold in winter, strong gusty winds on occasion). This is primarily a winter home so while it does get warm in summer, our primary concern is winter. We will likely be 100% electric since there is not natural gas and propane is not an option. That said, we will appreciate the expertise from this forum in advising on two topics:
1. Considering U factor, does it make sense to consider high performance windows and triple glazing?
2. The US window makers that i find, tend to have larger frames/mullions and are not as well insulated or sealed as well as those from Canada (fiberglass frames), and germany.  While our intent is to buy american, we simply cannot find excellent quality, low  U performing windows here. if stating manufacturers is verboten on the forum, please send me a PM on your recommendations.
Thank you for your advice, Steve

You might want to check out the specific Windows/Doors section of this forum.

Relative to chasing low U-factor (or high R-value) windows...that can be a highly debated topic... I will say that the best performance windows are an order of magnitude worse than even poorly insulated walls.

So we recommend maximizing windows were you will actually obtain a passive solar gain during the day and minimizing windows were you will not. We also recommend using insulated drapes at night that create several inches of air space between the glass and the drape, which will increase the R-value much more than the best performance windows.

As mentioned, I would go to the window forum and read the older posts/threads about windows. It will really help bring a lot of information to the table.

Since you are building a tight home (ICF), you have energy conservation as your goal. You are also in a Zone 4 climate area and having windows with a higher SHGC would be beneficial on your south elevation. I don't know your house orientation and whether it was designed to work with southern passive solar designs.

A lot of opinions out there but in the end, here are the facts; when you visit GBA (Green Building Advisor) you will find them using triple pane European or Canadian windows when they build high energy retrofit homes, new high energy homes and passive homes. Why? It's pretty simple. No American made windows really come close to the high end Canadian and European windows.

What kind of roof are you doing?

IMHO, if you are on a budget but still want high-perf windows, I would go with Intus Triple Pane PVC windows. If you have money to burn, you can turn to European triple pane wood/aluminum clad or Fiberglass Triple Pane.

thanks LBEAR and SailawayRB,
as you both recommended, i have started a separate thread on the Window forum where i also posted some recent links to window evaluations.

As Lbear suggests, many of the popular windows with Low U and high solar gain are either from germany or Canada. That said, there are others on the thread from colorado that are also viable. I hope for a lively debate since i have to select windows soon. We had initially looked at Serious fiberglass (based on feedback from Claire Anderson at Home Power magazine), but now the site redirects to Kensington PVC -- we are not interested in PVC.

Regarding Lbear's question on the roof, we are going with scissor joist, standing seam metal, sealed with r49 (probably spray + Batt) . Do let me know if any of this sounds poorly optimized -- we don't have "money to burn" as Lbear asks, and we are trying to spend wisely.
Thanks for the advice, Steve