Subaru Legacy rear suspension info:
1) All 95-99 L and GT models BOTH sedan and wagon, use the same rear struts.
2) ONLY 95 Outback models use the same struts as the 96 to 99 L and GT models.
3) All 96-99 Outback models use a TALLER strut than ANY other 95-99 Legacy.
4) All 95-99 sedans have a rear spring rate of 132 lbs/in.
5) All 95-99 wagons have a rear spring rate of 190 lbs/in.
6) ALL 95-99 GT and L models have one height of spring.
7) ALL 96099 Outback models have a taller spring than any other 95-99 Legacy.
8) ALL aftermarket OE replacement struts made are model specific.
9) They make a rear strut for the 95-99 L and GT models.
10) They make a rear strut specifically for the 96-99 Outback models.
Subaru Impreza WRX rear suspension info:
1) There are MANY differences in the WRX rear struts between sedan and wagon.
2) ALL 5MT sedans have a rear spring rate of 119 lbs/in.
3) ALL 4EAT sedans have a rear spring rate of 132 lbs/in.
4 ALL 5MT wagons have a rear spring rate of 132 lbs/in.
5) ALL 4EAT wagons have a rear spring rate of 144 lbs/in.
6) ALL 02/03 WRX have rear springs with a lower diameter of 150 mm.
7) ALL 04-07 WRX have rear springs with a lower diameter of 150 mm.
8) So, 02/03 springs have to be paired with 02/03 struts.
9) 04-07 springs have to be paired with 04-07 struts.
10) The BIGGEST difference sedan and wagon is the camber between the struts.... Sedans have more camber and sedans have less.
SO, WRX WAGON struts are CLOSER in design to the second gen Legacy struts than WRX sedan struts are... Anyone who says pair WRX sedan to Legacy sedan and WRX wagon to Legacy wagon is a complete MORON. ALWAYS try and pair WRX wagon struts to ALL second gen Legacy's. Just make sure that you keep the years paired between spring and strut. 04-07 WRX wagon struts are the best. They are closest in camber and have the highest spring rate of all the WRX models.
If that doesn't answer EVERY single one of your questions, let me know...
But, I have a question for you. And it's the same as John's.. What vehicle do you have now and what do you want to do with it?