Yes, 3G is based on very different HDMI chipset (2.0a). It does 10bit RGB. I expect it to work better, but with BM you never know
Price is good though.
HDMI Color Precision
10, 12-bit RGB 4:4:4 up to 1080p30, 8-bit RGB 4:4:4 and 12-bit YUV 4:2:2 in all standards.
is actually some prove that your current card simply doesn't support 10bit over HDMI (regardless what BM spec says).
It's because card doesn't support RGB ( maybe with exception to RGB 8bit as HDMI mandates this for any HDMI device) and because it most likely uses chip, which by the spec does not allow 10bit YUV 4:2:2 output.
3G model has also no 10bit 4:2:2 YUV (for high fps), but because it's 2.0 chip then it actually does 12bit for YUV 4:2:2 (+ it supports 10,12 bit for RGB <30p).
All of this is in line with HDMI 1.4.a (carried over to higher spec) spec which compared to 1.3a spec added 4:2:2 YUV "DeepColor" support as 36bit pixel format (so 12bit per channel).
So maybe current card does/could support 10bit over HDMI, but due to its limitation there is simply no HDMI mode which could carry this to your monitor. I think I've seen this on one of the AJA converters as well, where 10bit RGB was supported, but 4:2:2 YUV 10bit wasn't. It's probably all down to 1.3 HDMI spec limits.
Spec 1.4a says:
"YCBCR 4:2:2 is also 36-bit mode but does not require the further use of the Deep Color modes described in section 6.5.2 and 6.5.3"