In my experience, the cause of speed related vibration is wheel balance 95% of the time we get a complaint in the shop. Assuming the car is equipped with stock Saab alloy mags many shops will only do a static wheel balance, which means that counter weights are only used on the inside edge of the wheel. This is done for cosmetic reasons and in some cases because the wheel design doesn't allow for exterior weights to be used. This type of balancing takes into account 'up and down' movement of the wheel, or how oval the wheel is, but does not take into account the 'wobble' or side to side movement of the wheel. The result is that the balance readings on the machine will say everything is fine when in fact it is not. Often the effects are felt only at higher speeds.
Ask that the wheels be dynamically balanced with two planes of weights used, inside clip-on and outside adhesive used. (don't worry, the weights will be inside the spokes, not really too visible.) Dynamically balanced wheels take into account both the oval shape of the wheel as well as any side to side wobble and corrects for both.
If you are still experiencing vibration, roadforce balancing must be performed to rule out excessive wheel runout or defects in one or more tires. (new tires can be defective, too) Not many small shops have a roadforce machine so use this link to locate one. (larger dealers should have one, if they don't, stay away)
http://www.gsp9700.com/pub/search/findgsp9700.cfm
For those in or near Montreal, pm me as we are equipped with a brand new Hunter GSP9700 machine and I would be glad to balance your wheels correctly as well as align the vehicle if required.