My simulator can't read those files. I am saving simply text files with 0 for dead and 1 for alive cells. A 273x273 grid is quite large though, I think it will be slow.

Also, mine doesn't try to go as fast as possible. I'm just using a timer set at 100 ms interval which calculates the new grid every tick. I just tried a grid of 273x273 with 3x3 cells and it sure didn't run at 100 ms interval though. More like twice per second which would be 500 ms, so there's a large delay.

I wasn't saying my simulator was faster than yours (I didn't try yours yet), I am merely saying that painting just the changed cells will be hell of a lot faster than painting the entire grid.

Just for the fun of it I tried it again (273x273) without painting just the changed cells. This time, I am painting the whole grid each timer tick. It takes about 5 seconds to draw the new grid where it should run at 0.1 seconds.