Overall, I agree with @rleshner assessing the level of reserves for each market for the time being.
This has been an ongoing tangential discussion, but never really been addressed due to lack of research. I think extensive research should be done in the future to choose optimal rates beyond the finger in the air, but for now, synchronizing them as Robert proposed makes the most sense to me.
I like @Sirokko idea on the 100% reserves for ETH and BTC, but I do think that the competitive disadvantage would outweigh the potential reserve gains. I think the idea of 100% reserves will not sit well with the end user.