If you think ZX81 BASIC is slow, please have a look at ANDRE***'s nice programs.
ANDRE*** is from Canada and he loves it to program in pure BASIC and all his program run fast in SLOW-mode
I've created a small web-site with his software, you can even read his five ZX91 magazines, he issued in 1991!
Thanks for the compliments. I am working right now on the adaptation to the ZX81 of a game written by Paul Panks titled "DUNRIC'S 8K ADVENTURE". Not only have I adapted it, I improved the game. So the ZX81 versions is better than the original game, better than the Spectrum version.
If you want a beta version, drop me an e-mail. Otherwise you will have to wait for the final version to be made available at my web sites as soon as I am satisfied with the program.