This isn't a direct answer to your question but it might be anecdotally helpful. I have an older AEA DSP-2232 TNC, which was probably one of the best VHF/UHF TNCs made. It's a little large, but it works great. I've used it a bunch with HF Pactor and a few other modes. Lately, I've been using mostly soundcard modes with a DSP based transceiver. I've even been playing around with Winmor. It's a little bit of an apples to oranges comparison to your question, but IMO, I can't tell the difference between the performance of the soundcard stuff and the TNC. I think it has more to do with the transceiver's RX than anything else. But that's just my subjective opinion.