I'm going to try to get into contact with some manufactures this week if I have a moment, as many people will want to know this as well.
I have a busy week ahead of me so I might forget about this, would you mind bumping this thread tuesday so that I can keep you updated (and to be sure I'm staying on task).
I still believe that this card should go into your motherboard without a problem as many people would be on a motherboard similar to your, not to mention a huge public out cry. Also think about it this way, if PCIe 2.0 was not backwards compatible nVidia/ATI would be severaly limiting their possible market for these cards.
Till I see conclusive evidence I really don't want to suggest anything, partly due to this conflicting evidence you keep finding, compared to what I have seen as of late.
Right now the only major difference between the two slots 1.x and 2.0 is the difference in bandwidth and increase in watts that can be supplied through the slot. Both of which are not factors yet.
I think it will work, but want to confirm this.