Intensity Shuttle doesn't actually support 1080p60 so you won't see those clips!
And for obvious reasons, two pass encoding can't be done in real-time. In actual fact most x264 GUIs now use CRF encoding instead of two-pass. CRF aims to encode every frame to the exact same quality level, so bandwidth adjusts dynamically, and often radically, depending on what it has to compress.
This is the kind of flexibility that a hardware encoder simply cannot match. Every cheapo hardware encoder I've seen essentially seems to be CBR based to all intents and purposes. The last one I looked at in Avermedia's Game Capture HD was extremely basic and produced icky results.