honestly, no i haven't heard a tempest, but IIRC the Vega has more 1-way excursion. 18mm is about .75 of an inch.
lemme find the Vega site..

http://www.cerwinvega.com/products/mobileaudio/index.html

scroll down, either the 154 or 15D4

combined excursion of 1.6, so .8 inch each way, just a tad more than that tempest.

read up on it though, 500W at 96 db is insane. what is the sensitivity of the tempest, out of curiosity?

What do you mean, rhetorical question? 1998.5 SVT --> http://www.cardomain.com/ride/2155561/1 #4619 of 6535, born Feb 18, 1998. i'm a smarta$$, don't take it personally