My Single has been running for 2 weeks, has a total average of 865.3MH/s, and a U:12.04/m. That means that it takes ~71.86MH/s to get 1 share per minute. So yes, 1.00GH/s should get you about 13.9 shares per minute.
Now that's assuming diff=1 shares. If you're running 7.18GH/s, but your pool is set to only accept diff=100 shares and above, you will get a U:1.0/m.
Lastly. If you had one GPU @ 500 M-KH/s and it submitted say 5 shares per minute. The second GPU is @ 600 M-KH/s and submits the same 5 shares per minute. All other things being equal; these are "effectively" the same then right? Even though hash is different; or am I missing something.
Yes, your submitted shares is all that really counts. If you're hashing at 10GH/s, but not submitting any shares, it's pretty much useless efforts. That said, share submission is pretty predictable based off a given hashrate, you just gotta give it enough time.