SCSC4

I am looking to up grade my factory size tires and rims on my 95 SC400. I have done a lot of searching and I know the basics, bolt pattern, offset ect. I would like to go to a larger, wider tire. It seems to be popular to say "what is the widest tire I can put on my car" without any regard to how it will perform. I want to put on different tire not just for looks but for performance. (After which I plan to upgrade the suspension) but I am concerned based on some of the posts that if you go to wide a tire then the car doesn't drive normal, you get heavy steering and funky steering in the groves on the freeway ect. I just don't want to go out and spend thousands of dollars and be unhappy on how the car ride and steers. I wanted to go with either 18' 10 in the rear and 8" in the front or 18' 9" wide all the way around. What is anyones experience with these different spec and how did it effect the handling, steering and ride. I don't know if I am explaining myself very well but any input from the gurus and people who have done something similiar would be greatly appreciated
Thanks