I'd be interested in helping you test your code as I have a 690GTX that is begging to be spun up for Litecoins!
One thing I was curious about is the new "Shift Left" (SHLFT) instructions in the new Kepler architecture and how it might be used to juice even more performance from a pure CUDA based miner.
For integrating my CUDA code, I briefly looked at the source code of the reaper GPU miner, but I do not really like it. Looks like a hack.
I only know about a SHFL instruction, which is for intra-warp data exchange (shuffle?). I do not see this speeding up hashing at the moment.
But the new 64 bit funnel shifter is only available in the 3.5 compute capability, as offered by the Titan card, or the GF110 based Teslas. Lesser Geforce cards like your 690GTX have compute 3.0 only. A question on stackoverflow deals with this feature:http://stackoverflow.com/questions/12767113/funnel-shift-what-is-it
. It has the potential to somewhat speed up SHA-256 and scrypt hashing, but the price of the cards is just way too high.