I had a bad experience trying to get any technical data form the Lowe's salespeople. They knew very little about their windows and windows in general. I talked to two different people who worked in the window department on two different days, with no positive result. This experience scared me concerning what their installers might be like, so I ruled Lowe's out fairly quickly. It sounds like you had a similar experience, since they didn't know the u-value of their window. I would suggest don't buy unless they can provide you one and deliver the window with the NFRC sticker attached.
The main problems I hear with Lowe's are hit and miss installers - not as much that the windows are always poor quality - just not usually mid-high end either. Most of the people who hang out here are very into windows, and lean towards higher quality windows more than the low end stuff, because they believe they save money and trouble over time. You'll have to make your mind up yourself on what you can pay, and what you think it might save you going with higher quality windows. The Pella Thermastar stuff from Lowe's looked of reasonable quality to me, but the Simonton stuff from Home Depot looked better (neither had exceptional warranties). I recently saw the Bayshore, which looked even nicer. I'd say the Bayshore price you got is fairly good. The Great Lakes dealer in my area is a lot more expensive for those.
I have not looked closely at the American Craftsman and Reliabilt windows to comment, but I guess one thing to consider are the things that the data you listed does not cover such as warranty, quality of the PVC over time (is it virgin uPVC?), installer quality, long-term stability of the window, air infiltration numbers, DP-rating, reinforced vinyl, BBB ratings, the extra value of moving to a super spacer or TPS seal, etc. NFRC numbers do a good job of suggesting initial energy efficiency (with the possible exception of air infiltration), but there isn't a similar set of numbers for overall long-term quality of a window, installation, or the quality of a warranty (except maybe length
). Those type of things may make the difference in your choice, or will be an advantage of moving to the higher-end windows.
Make sure to compare quotes as an installed price and with tax, etc. Good luck window hunting!