addition of weight to parachute.. linear or not?

Well, for my assignmetn we have a parachute, our testing hasnt been thorough enough to determine fully the effects of our three variables , which are:

change in surface area

differnet shaped parachute with same surface area

addition of weights to the parachute base

Well the change in surface area is alright, but the different shapes we have, a rectangle, circle and triangle. aafter testing them the time they took to be dropped from 2 stories high, they all took around about 7-8 secs long, but it was a bit windy and results are not very accurate, we didnt have long either in class to do it.

What im asking is, 2 things, should the three shapes show different results, if they are all the same surface area would the different shape make the parachute slow down or speed up at all??

and.. say that the parachute weighted 10 g, and it took 10 secs to fall, we added 10 g, so it weighed 20g, and it took about 8.. we aded 40, and it took about 4 or so? i forget, but would the addition of weights if we graphed the time each parachute took to fall AGAINST the weight of the parachute, would it be linear or not? just some help appreciated because our results are fairly inaccurate and not much time left, thanks guys/girls.