why do you need a graphics card at all, it's only going to use power up.
I imagine that the OP is planning to make use of the incredible parallel processing capability of a powerful graphics card to power his distributed computing system. Since a GPU when run properly can be orders of magnitude faster than a CPU in these kinds of tasks, it does make sense.
Here is the CUDA based version of SETI@home, they advertise it as:
This version runs from 2X to 10X faster than the CPU-only version. We urge SETI@home participants to use it if possible.
As for the graphics card running in a PCIe v1 x16 slot - this will be fine. This slot has the same bandwidth as a PCIe v2 x8 slot - and according to
these tests the performance dip in a top-end GTX 480 is tiny.
However, I would suggest against supporting the SETI program,
bad things could happen