I just reread this thread and finally get it that all OP is really concerned with is the protocol version for PCiE. If I understand this correctly I'd encourage you, Eeyore888, to consider that this is an exercise in futility since it really wont matter in Linux nor Windows. There is simply no way that the 970, let alone the 670, (actually not even both combined) can saturate the PCiE 2.0 protocol. In fact it is highly unlikely that both in SLI could saturate 1.1 !! This, with your current setup, is simply a non-issue.
Even if you had a pair of GTX 980's in SLI you would be hard pressed to detect any difference on most games between PCiE 1.1, 2.0, and 3.0. Since you don't have that monstrous hardware and are on 2.0 this again is a non-issue.
One important thing to consider beyond bandwidth availability is the data pathways from GPU through PCiE to CPU and back again all relying on the operating system's kernel. Even a stock Linux kernel has 1/3rd to 1/5th the latency ( transfer delay ...lag ) of the best Windows kernel. A high performance, realtime, low-latency kernel has 1/10th to 1/20th the lag of a Windows kernel. This only adds to what you feel as performance rendering the difference all but unmeasurable by any means except on the absolute hottest hardware under the rarest most extreme software stresses currently available.
I have no idea what nVidia will use for a model naming convention in the4 future but whatever they name it, it will have to get to at least 2 more generations IN SLI for there to be a noticeable difference between 2.0 and 3.0 PCiE.
If you'd like to see some in-depth, correlated testing of just this subject take a look In-Depth Comparisons 1.1, 2.0, 3.0
Note that his testing is in Windows only but his measurements do encompass the lag of the Windows kernel. Unfortunately MS does not offer a Hi Performance, realtime, low-latency kernel and Linux doesn't have compatibility with this level of DX11 games so we are left with extrapolation instead of hard numbers, but the progression is nevertheless clear.