We acquired an FT450D a couple of months ago. This is an excellent radio: it copes with HF signal levels better than the FT817, and seems to have more "punch" in its audio that the 13dB increase in TX power would suggest. I wonder how much of that involves speech compression on TX - nevertheless the results are good.
Connecting it to a PC for CAT control should be straightforward: it does after all have an RS232 interface on the rear panel. It turns out the radio requires that RTS be asserted, or it won't respond (not unreasonable, seeing as that's the purpose of the pin). The cable I've ended up with is as follows:
Using that cable, Ham Radio Deluxe is able to take control - as expected.
On data modes, the radio appears to work well. Ham Radio Deluxe's data mode program "DM780" was able to demodulate several PSK signals using my FT817 data interface, although the signal level looked a lot lower than it should have been. Even the PC microphone picking up audio from the speaker was successful.