I'm no expert....but the theory is like this I think. LS/VTEC increases rod length, giving more time to pack in fuel and air. The result is higher piston velocity and more power.

But, the rod angle increases, which introduces more stress and wear. It's my understanding that this is why some of the swaps fail after 20K miles or so...

So use quality parts, and if you don't know what you're doing (sorta what Snoopy said in a nutshell) you're going to end up with a horror story to tell.