* PAGING jrients *
Your post inspired me to track down some of those Pegasus back-issues. The "Gateway Quadrant" column Pegasus' 5&6 summarizes the different Traveller products offered by Judges Guild - number 6 includes a tantalizing, too-brief selection of TAS-like news bulletins relating to Ley Sector.
The Pegasus 7 column is a stat-lite discussion of aliens from different novels - interesting as far as it goes, but not specifically dealing with the Gateway.
Pegasus 8 contains what is billed as a "part one" on gas giants, specifically Jupiter and Saturn, offering some general ideas for sci-fi RPG planet building - the author, Dave Sering, alludes to a "part two" dealing with the outer giants, and perhaps additional articles on the terrestrial planets as well, but as far as I can tell from the index, these were never published.
So, not a lot on the four JG Gateway sectors, unfortunately. Remember that JG published several adventures set on different worlds in the sectors, and they are available pretty cheap from the various second-hand vendors, often still in the shrinkwrap. I have Rogue Moon of Spinstorme, and I plan to pick up Tancred and Corsairs of the Turku Waste eventually.
As an aside, Pegasus 3 includes an article on Traveller ship combat with some interesting variants, such as "Detect" programs that are used to represent ship's sensors and a new way to handle LBB 2-style battle damage.
I hope this capsule review is of some use.