how I have a feeling that your card is not ok. Either drivers are wrong or the card has a problem. Just thinking...you have tested it in several hw configurations and its always slow...
Ok. In general, most of common technical problems solved by someone, can be found in youtube. Did you try put words G27 CENTERING in youtube search box? It gives at least four video promising fix for centering issue.
Have you tried to steer full to the left, then full to the right? I need to do that every time I start driving LFS, otherwise my wheel centering sucks (I have G29)
I think if he buys the license that costs same amount that the value of the voucher, he can pay the license with the voucher in the checkout page. This is just a guess.
I know nothing about optimum, but my current HW is i5 4460, 8GB DDR3, GTX 1050. With this I play succesfully LFS (with one screen, I believe more screens would run aswell), Assetto Corsa and Raceroom.