FABIO wrote:

Instead you die in about 5 seconds to concentrated fire from everyone but the one squad you tie up in melee. You might get lucky and kill one marine in that time. It's actually less expensive to just buy the jetpack upgrade and suicide bomb your orks into marines.

I've tried games where I went assault marines/stormboyz heavy against tac marines, and I only came close to winning when I had them matched 1 for 1 which is almost impossible due to the cost. Not only does it massively slow down your teching, it gimps you in the long run since you'll be stuck with jump troops of questionable use in later tiers while your opponent will have upgraded tac marines carrying him the entire game.

The only real use for stormboyz has been getting the jump on heavy weapons teams, and even then only if you have the Warboss since the Mek and Kommando can do that job just fine.