yeah, most likely death will be instant. try not to land on your legs, make sure there are no bushes or trees or below. bit more than 100m high (i think you'd jump from the street and not these towers), should be letal.
try to check it out to find the ideal place to jump. are there any fences? people who might stop you? pictures may help.
remember that sometimes misfortune may make your plans fall through.
yo, good luck, safe travels and enjoy your flight ^^