I've had an Infinito for two years and absolutely love it.
I chose it for Outlaw 2010, and it has done me proud in each one since then. The first time I used it for a race was my first ever tri, Swashbuckler, and I was amazed at how fast it was. But so comfy!
I also use it for local TTs (10 miles) and it's great for those too.
So a big vote for the Infinito from me, though I confess to knowing nothing about the Sempre!