The difference between a Tbird and the old slot athlons is where the L2 cache is and how much cache there is. A Tbird has 256K of L2 Cache on the same dye as the cpu circuitry, the old athlon has 512K cache on seperate chips. This allows the L2 cache on a Tbird to run at the same speed as the CPU, where on an old Athlon it runs at 1/3 the speed of the CPU. The Tbird would be the better choice.