I assume you're playing single player against AI?  You might consider downloading some of my custom maps.  A few have chokepoints.  Especially the one called Ring of Risk.  Also try Gateway to Paradise.  It's an auto-install file that will put the maps in the right place and they'll show up as "Galaxy Forge" maps in the game's map browser.

http://tinyurl.com/Sins9

The best choke points are at stars (if you have entrenchment/diplo/trinity) because you can put down 4 star bases. That should be overkill though.

Douplegangers is a realitively small map where each player has there own solar system. Only one that's coming to mind atm.

Try Fulcrum. There is only one star and one gas giant separating the 2 sides.

Given the antimatter regen bonus of stars, I find that you're better off buying carrier cruisers and parking them next to the bases than buying these upgrades.  You'll get more strike craft that way, you can redeploy them for offensives, and because of the star antimatter is irrelevant.