Is there any major advantage of using the GBIC ports for stacking over the regular gb ports (24 and 48 I beleive?) in terms of performance, stability, etc?
So to answer the question simply, there is no extra benefit in using mini GBICs (SFP) compared to a CAT6 cable to connect switches together in a stack. Both copper or fiber connections will sync at 1000Mb/sec.
The only benefit of using mini GBICs or SFP;s is if the connection between the switches are beyond 100 meters or 328 feet.
But I am more than happy to connect switches together with CAT6 cables for stacking purposes, it's more cost effective.