.. in the newer version you have to use the "launch Bitcoin client as server" option ..
Not only in the newer version, you always had to run the client as server when solo-mining (or to use JSON-RPC).
.. I've left the client on overnight and so far I have generated no bitcoins at all ..
Well, you probably won't generate any bitcoins ever.
Let's face it,
your 6970 might run at 400MH/s,
at current difficulty it would take about 400Days on average to solve a block,
so even if you're lucky you might not get anything for about 1year, not to mention that within that year the difficulty will probably rise.
That's the reason why pools exist, most miners just don't have enough hashing-power to mine on their own and get anything at all.
GUIMiner is reading I'm generating around 300khash/s even though I have a 6970
Are you sure GUIminer is actually using your 6970 and not only your CPU?
Anyway, as stated above it's not really worth solo-mining on a single 6970, not even on 2, 3, or 5 of them, except you don't expect do get anything back/count your hashing-power as donation to the network.