Would I notice much difference between the 1.9 and 1.98 rockers provided I have a VT Series II berlina Ecotec V6?

You would, however roller rocker ratio selection would come down to what best suits our requirements. For arguments sake, if you tend to spend most of your time in the low to mid or mid to top end engine operating range, then you would go for the 1.9:1 and 1.98:1 ratio rockers respectively.