PCIe 2.0 to PCIe 1.0 Crossfire will there be any issues

[Jvfrank04]

i want to try and crossfire two ati radeon 5770 cards on a MOBO the has one PCIe 2.0 and one PCIe 1.0 will both cards default to 1.0

 

[dividebyzero]

You might need to be more specific.
I don't think I've heard of a motherboard that natively takes a 2.0 spec lane (500MB/sec upload/dl per lane) and splits it to 1.0 (250MB/sec upload/dl per lane) - that is usually the function of an onboard bridge chip (or lane extender) such as Nvidia's NF200.

Now, taking your comments at face value -although if you could post the motherboard vendor/model it would certainly help- then it is likely that the PCI-E lanes would be 1.0 spec.
The bright side is that, the HD5770 doesn't use enough bandwidth to make any difference whether the lanes are 1.0 or 2.0 (or 3.0 -soon to be added), unless the slot is labelled PCIe x16 but is actually x4 electrical (or lower).

 

[teklord]

Never heard of a motherboard using two different PCI-e versions. Most likely it splits the lanes into x8/x8 for multi-GPU. Shouln't see any performance loss with HD 5770 in CF with x8/x8.