Can I put a 1TB HDD in my optical Bay
Yes.  You can put a 1TB drive in there.

The port that your optical drive connects to is a standard SATA III port.  This is why you are seeing that it supports 6Gb/s.  The "negotiated" speed is the speed at which the device will communicate.  A SATA I drive has a transfer rate of 1.5Gb/s.  So, even though SATA III can go 6Gb/s, a SATA I can't go any faster.

A SATA III port is backward compatible with SATA II and SATA I.  That being said, a SATA port is a SATA port - it doesn't care if you are attaching a spinning hard disk, an optical disk or an SSD.  SATA supports 48-bit LBA (Logical Block Addressing) which means your drive can be up to 128 PB (Peta Bytes) or 128,000 1TB drives.  So, there is no limitation from a hardware standpoint.

I have personally [used this model optical bay drive caddy][3] with a 1TB drive with no problems.  The specs say "up to 500GB" but I suspect that since this product has been out for such a long time, they just never bothered to update the marketing material.