can you post more detail of your system, motherboard model, psu, and cpu ect. so we can check if its actually limited to 1.0x16
if you budget is 10k and wanna the best card the in theory a 590 or HD6990 works with 1.0x16,
or you can get any entry level card since the motherboard is obviously old and bottleneck it.
or invest in a new system altogether