If I were to play Tyranids, I'd be sure to include Gargoyles. Players with assault armies tend to be primarily concerned with the raw power of their models, rather than the tactical finesse it requires to deliver them. If you have a unit of gargoyles, which are quite fast and are relatively cheap for what you get with them, you can use them to pin down an enemy unit for a turn while your hormagaunts and warriors charge across the table. It's the same concept as using a Lictor, except you're using at least ten models (and more is always better) instead of just one to three.
I actually think I'd make a good Tyranid player... I just don't want to deal with storing a Tyranid army... friggin' 150-model armies, man...