Hi, Karen. Can't help you on the soy gel. I use Citristrip almost exclusively but have also used Peel Away. Depends on the number of coats of paint requiring removal as to which I select. For a moderate amount of paint, up to 10 coats or so, Citristrip is my choice on the factors of safety, reliability and availability. For a really heavy paint build up, Peel Away is my choice. They both have web sites and you can check them out at www.citristrip.com and www.peelaway.com.
So you are aware, I answer most of the posts at the Citristrip site but this is a totally unpaid deal. As far as I know, no one is paid for their answers at the BV site that you are on now. Hy will probably post more here about Peel Away and he is involved in the company but that certainly does not make his information wrong, just a little biased sometimes.
At your home center, you can buy a special saw made for getting the old paint out from windows that have been painted shut. This can be a big help or you could be wondering why you are messing with it. It just depends on how much paint buildup you have between the window stiles and the window frame stiles. All that I can say further is to be careful trying to get the windows to move again because you could break some wood that will be difficult to replace or get cut by breaking glass. This is not a job that I would tackle lightly. Remember that the paint dust will have lead in it and take the appropriate safety precautions for this.
Whatever you choose for stripping the paint and old finish, be careful with this also. Read, understand and follow the instructions and safety information that comes with whatever products you choose and follow the HUD guidelines it they are more restrictive.