As far as tai otoshi and harai goshi being good for bigger, stronger opponents... I'd agree and disagree with that. Those are great throws when you're very proficient with them. Timing and kuzushi have to be excellent to make these work on a bigger opponent. You can't fly in and muscle them around. Since they have a size and strength advantage, either your placement has to be stupendous or you have to set it up with a combo (ouchi gari, etc...). I'd really stick with sacrificies, sweeps, and leg/ankle pics until you get very comfortable with a deceptively complicated forward throw like tai otoshi. Like someone mentioned above, drop seoi nage is a great throw for someone larger & stronger. Get him pushing on you and let him develop a habit and comfort with plowing straight forward. Attempt several rear sweeps. When ready, fake a rear sweep. I like kouchi gari for this. When he steps back or raises his leg to avoid your "half-assed" attempt, that's when you drop. Remember to drop deep between his legs, not just straight down. Done right, you'll almost always get a score out of it.