Best passive Fusion / NSK2480 HTPC graphics card?

[Spod]

Hi,

Long time no post, but I've a question that I've struggled to find an answer to.
I'm running Windows 7 Media Centre in an Antec NSK-2480 (same dimensions as the NSK-2400 and Fusion), using an Athlon 4850e CPU and integrated AMD 690G (Radeon X1250) graphics.
I'm finding the de-interlacing isn't perfect, and I'm getting huge lag between pressing buttons on the remote and seeing the corresponding update in the Media Center menus. (Sound response is immediate, but it can be seconds before the screen catches up). ATI isn't releasing any Windows 7 updates to the existing Vista Catalyst 9.3 drivers for this GPU, and drivers are what fixed this issue for others, so it looks like the only solution is to add a graphics card.

I'm not planning to game on this system, so 3D speed is fairly irrelevant. I just want better Windows 7 drivers and video playback.

I'm very keen not to add any noise to the system, so I'd prefer a passive card. I also want native HDMI with sound, which seems to rule out Radeon 4650 cards - I've only found 4670s with HDMI built in. But the passive 4670s I've found all seem to have heatsinks too tall for the NSK-2480. The 4550 doesn't have the same vector de-interlacing as the 4600 series, though I don't know if the difference is significant. And unless you're using Linux, in which case nVidia has better hardware video decoding, no-one seems to like nVidia for a Windows HTPC - all last gen, too hot, too slow, and not as good decoding as the latest ATI cards.

So, is there a passive 4600 series with HDMI that fits in an NSK-2480? If not, what compromise should I make? Get a fan? (Dual slot is fine) Get a 4550? Get an nVidia (which one?)

The fan would have to be totally masked by the two Antec tri-cool fans on low (no CPU fan, using passive ninja mini).

Thanks!