I have the billet steel 1.23 ratio rockers on a cam which I believe is the stock vegas 460 cam? Pulls smooth to well over 6000rpm on a sprint track, but the power is probably all in before that.
I did use the same rockers on a stock cam originally for a short while, just gives a little bit more everywhere. The stock gx390 cam comes on harder than the vegas cam in the 3-4000 rpm range but dies off quicker. The cam with just a little bit more duration really smoothed out the power and made it more enjoyable to drive.
For the price of the vegas cam ($50?) I would put that in first, and add 1.3 rockers later if you find yourself wanting a little more. I've got the springs NR sell, 55lb I think. Overkill but they haven't caused any issues.