Most restrictive part of a G's exhaust system?
 

I am considering running test pipes with a good y-pipe and that is it! Will this be beneficial? I might add some headers in there.....just not sure.

IIRC:

Restriction on stock exhaust system

Cat > Y-Pipe > Mid-pipe back > Header

I think you will notice a decent improvement replacing the cat and y-pipe. Be sure to hear the test pipes first though. You will get significant rasp with test pipes.

i figured most of all cars the most restrictive part of the exhaust was the catylic converters

Remember, most aftermarket Y-pipes aren't really ment to be used with a oem mid pipe no matter what they might say. A 80mm output into a 65mm oem mid pipe creates a 1/4" abrupt wall in the flow path. Tanabe's Y-pipe has a 70mm output, maybe some carefull grinding on the oem mid pipe inlet can smooth things a bit, just a thought to those that won't replace their oem mid pipe with a aftermarket one.

Cats, then y-pipe or headers, then cat-back exhaust.....

ditto on that... i was running a Fujitsubo Y-pipe (with header and cats) which is 86mm outlet into the ~60mm stock midpipe.... big restriction in my flow, and you should have seen the ring of nastiness on the midpipe flange when i finally got the Legalis-R installed.

if i had to do my entire setup again, i'd to high flow cats, y-pipe, and exhaust. the headers were a major PITA and $$$ to install

If you're going to stick with the OEM mid- or rear-section, at least make use of a reducer cone to avoid the abrupt wall/transition others are talkinga bout.