Hardwareoverclock.com takes a look at Radeon HD4890 Crossfire performance in Games and Benchmarks.
>> Radeon HD4890 crossfire performance
A Radeon 4890X2 will never release, it is fact. The high temperature of the chip and the voltage transformers makes it impossible. But 2 Radeon 4890 in Crossfire are possible.
>> Radeon HD4890 crossfire performance
