The 156 Sport is the run off model of the 156, which saw about 110 produced. I believe all of them were grigio Stromboli metallic grey, with dark grey leather with 17 inch multi spoke alloys - they usually had plenty of spec including dual zone climate control, the lowered sports suspension seen through the range under different headings, electric windows all round and so on; with thing like BOSE sound system and rear spoiler etc being options.
I had one before doing the switch to a 159 and the difference is certainly in the weight of the thing. They worked really hard and used a lot of expensive alloys and production methods on the 156 to keep the weight really nailed down, where the 159 was designed more with the American market in mind and was more about cheap fast production and predominantly comfort, so the 159 is more akin to the 166 in my eyes than it is the 156.
so I do agree with you the 156 1.9 does feel faster and more nimble than the 159, although the 159 does feel more robust and tightly bolted together than the 156 but its nothing to do with the factory map or anything, just the weight factor.