It's a 1x to 16x powered riser, this one:
An yes.. I too and seeing a real delay with BTER deposits as well.
what was your command line when launching cudaminer with the risered card? if you've been using -H 1, try switching to -H 2.
Maybe the x1 bus conneciton was beginning to limit the hashing speed, so the benefits of any additional overclock were lost.
Christian