... in no particular order of importance...
The super-G or Pre-N stuff is a proprietary extension of the .g standard. In order for it to work, you will need to buy the same brand for both ends, i.e., a Pre-N router/access point and a Pre-N adapter for the computer. They are not mix-n-match. If a ''foreign'' adapter joins the mix, it will all drop back to standard .g.
The increased speed of these brand-specific ''solutions'' is useful only for within-network file transfers. You might get something closer to the speed of a wired connection which will make moving large amounts of data more efficient than with ordinary .g equipment. However, your internet connection is still whatever it is - probably 1.5-3Mbs for the average DSL or cable hookup. That is 1/20th of the speed of the Pre-N/SuperG reasonable expectation in real life. It is 1/10th of the speed of standard .g in real life. So the true limitation is not your wireless network, it's your fundamental internet connection.
There is no measurable lag from wifi by itself. All lag occurs on the other side of your modem. However, the wifi stuff is all subject to radio interference from other nearby 2.4Ghz devices, such as microwave ovens, cordless phones, baby monitors, etc. It is also subject to signal strength degradation from material (walls, floors, trees, etc.) located within the direct signal path. Thus you may need to play around with locating the access point and the client antenna until you achieve a satisfactory result. The Pre-N stuff is reported to have a strong signal for good distance and penetration. But all that could be for naught everytime somebody pops some popcorn in the microwave, or the neighbor answers his cordless telephone which you have no control over. Just one of those things, you might loose the connection for no apparent reason.
dw