Stock cats generally get really clogged with crap, so I say any change would be a good change. You could also just find a cheap cat and use the straight pipe untill you must check the car's emmissions, then switch back.
You have the muffler cut off right, with just a straight pipe? If you made a straight pipe for the cat too, it would support enough exhaust flow to run some more modifications without buying a standard exhaust.
$300 for a Cat? Don't buy it...there are good ones for under $150
'90 AWD TSI: 3"TBE, FMIC, 7cm ported 2G exh. mani, TO4B 50trim, 550's, 255lph, -6AN from filter-rail and rail-AFPR by Aeromotive, AFC, 2G MAS and 3" intake, Pocketlogger. Sold
'92 AWD TSI: 6Bolt/4bolt (March), 2G MAS, Home made 3"=2.25" intake pipe. Ported O2 and amazingly uncracked 1G mani to 7cm, no cat, straight 2.5" in place of muffler. XTD 2200lb PP and 6pck sprung disk, Walboro 190, 550's, pocketlogger, ebay MBC, SAFC, MHI EIII16G.