I think this depends on how you ride. I race harescrambles and have the YZ cam. It is a noticeable improvement over the stock cam, but I am going to give the '06 YFZ cam a try. Even though I race in the woods I typically rev the bike out, which I think the YFZ cam is better suited for.
I would agree. I always rode big bore motors with tons of torque and never was big on revving out the bike. I won my gncc championship on a 525 KTM. My biggest downfall with 450s is I want one that has the grunt of my old 525. VERY tall order for a 450. I had a Wiseco cam in my bike when I got it and it felt like a dog to me. Was it really? No probably not just all the power was in an rpm range that I never rode in. Putting that yz cam in put a lot of bottom end and mid in so that when I busted the throttle out of corners the front end would pick up and go. Combined with the fuel injection letting it get to the rpms a little quicker it really tricks me into feeling like I'm not far off from the torque I had. If you do like to rev a lot though I would probably take JDstang's advice and try another cam first.