First, I'm not sure I've found any public documentation on this. I'll have to check with some IBMers, but here is where I am going with this. The Connect Web API isn't a replacement for STLinks, but sure seems like a good candidate for exploring alternatives to the STLinks architecture.
Everytime you access Portal, a multitude of checks occur to determine if the logged in user is "Sametime capable". If so, the STLinks applet then loads and viola, awareness, chat, endless chat requests for your help, etc. If you're using dual directory - more overhead. The most common "statement" I've heard is that once an admin enables Sametime, performance in Portal is degraded. This isn't surprising, but could the Sametime Connect Web API Toolkit could be the performance capable alternative.
Likely the first obstacle to this is entitlement. There's a reason you're using STLinks and not the Connect client. If I am not mistaken, the Collaboration Accelerator package for Portal gives you web capable chat, but not the Connect client (I don't sell it, just support it). So if you've got a Connect client, it would be extremely interesting to do a conditional check to the Connect client and if present, use it rather than calling the
I'd like to explore this in more detail, but if you have already experimented with this, post a comment.