You will not be able to connect a T1 directly to a PIX firewall. Although the physical connections might match, it will not work.
You can interconnect the pix and a router terminating the T1, both sides are using ethernet then. (this is probably the situation that you have?) It will make no difference whether you use cat5 or cat6 for this link.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...