delly,
There is a few different ways to approach the xXx upgrade, but a very common one is to go with a Super G Carb if you have A Super E. If you are going to go from E to G, you will need a different intake and as far as I know xXx does not provide that, thus you need to find one (evay are good sometime). If that is the case you can obtain the carb complete from xXx with the G, get it in and then send them your E and get refund.
What others have done, is stick with the Super E and just order the xXx Super E carb complete from xXx. When you get it, remove the restrictor plates on the intake (if it was not already done with like a exhaust change), install the new Super E xXx, mail them back your old one-get refund.
Fine tune the Super E as needed.
If you have not done a great deal of mods to the Engine (head, decking, bigger cam, etc). The Super E will give you a better overall ride carb. The Super G is better for the top end and high performance but allot of that benefits will not really come into play until you get it up on the upper end.
So if you want to smoke tires easier, lift the front, get that surge of power when you nail it more, The Super G may be the way to go, however if you are going to do that, it may be a good time to think of other mods. If you want to just get some decent performance over stock along with good overall ridability on the road, Super E with a xXx should do you fine.
Oh the xXx is offered in chrome and non-chromed and though I think the overall consensus is that the chrome from xXx is good, there can more issues with such. S & S does not recommend chrome due to increase possibility of erros from weaking the metals during the chrome and more likely have the process get in very small areas that could effect the tuning and operations.
Good luck with what everyway you go.