No, they are not all the same, each level V6, GT, Shelby, gets an increasingly better shock/strut package. And yes, aftermarket stuff, depending on the brand, can be a huge improvement over stock.
I am not sure if they have changed their build specifications for standard production, but at least for the 05-06 I am fairly sure their spec sheet has remained the same. If that is the case there is no distinguishing difference in the models as listed in the spec sheet - screen shot of doc in Word format attached:
As for aftermarket, most yes; however, you will want to compare the piston and rod specs of each. Adjustable damping is a huge + over stock non-adjustables depending on your driving style and end use.
Attachments
Spec Sheet - All Models - Shocks-Struts Rev 04 Build for 05 Model Year.doc
LV51ER - Yes - as of the 10/04 build spec sheet the primary supplier of shocks for the S197 was Tokico.
Riggs - if you are asking about the non-adjustable Steeda Pro Action S&S then yes, they appear to be an option; however, without looking at the design specs I can't tell off hand if they are truly better than the stock Tokico. making a "loaded" statement like this:
"...engineered by Steeda and manufactured to provide the ultimate in ride quality and handling while exceeded OE standards for durability and build quality."