The 500MHz and 300MHz are valid HT frequencies
Table 59. Link Frequency Bit Field Encoding [FreqExt, Link Frequency] Transmitter Clock Frequency Encoding (MHz) 0_0000 200 (default) 0_0001 300 0_0010 400 0_0011 500 0_0100 600 0_0101 800 0_0110 1000 0_0111 1200* 0_1000 1400* 0_1001 1600* 0_1010 1800 0_1011 2000 0_1100 2200 0_1101 2400 0_1110 2600 0_1111 Vendor-Specific 1_0000 Reserved 1_0001 2800 1_0010 3000 1_0011 3200 1_0100 to 1_1111 Reserved * These frequencies were defined in revision 2.00 of the specification but are redefined electrically in revision 3.00. The presence of a Gen3 capability block indicates that a device implements the Gen3 electrical behavior for these frequencies. Gen1 and Gen3 devices are not interoperable at these frequencies.
Check http://www.hypertransport.org/docs/twgdocs/HTC20051222-0046-0035.pdf
For details
Thanks, Rudolf