Trivent Sport vs. Expert

Hi all,

I finally got a really good fit done and what's encouraging is that the reason my left knee hurts when I ride is clear. The downside, however, is that I really need a new pair of shoes to fix it. I was told that Specialized is the way to go for the shims, etc I'll need (anything in the BG line). The guy also told me, if you're going to do long course triathlon (IMAZ this year) then get the gear for it and consider a tri shoe.  That being said, he doesn't sell gear, so I'm fairly comfortable with this recommendation.   I don't mind spending the extra money up front if the alternative is in a year I'm going to wish I'd purchased the expert.  I'm not the kind of person who has to have the latest/greatest.

My question is simply is the difference in stiffness between the expert and the sport worth it? Here's information for those not familiar:

Sport: http://www.specialized.com/us/en/bc/SBCEqProduct.jsp?spid=57810

Expert: http://www.specialized.com/us/en/bc/SBCEqProduct.jsp?spid=56684

Thanks in advance!