Displaying hex is quite fast (compared to trying to display decimal), though you're right that it might add up to a noticeable amount of time in the end. I did the full million digit calculation on that sample page on the same computer and it took a little over two hours (so 2.1x slowdown) but at that point I was also adding a 5ms delay every 100 terms.

It is fun to scroll down and watch the "cutoff", where digits above that are not changing and digits below that are. That's just as fun in hex as it is in decimal. But yes, maybe I should add an option to turn that off.