Hey yall. I have a old EVGA p67 FTW that doesn't have pci exp 3.0

I'm getting a 1070 and eventually likely getting a second to SLI.

I've been holding off upgrading as i'm just out of college and don't have the money. (Plus my old i5 sandy bridge is OC'd and doing just fine!)

Was wondering if the performance loss from my inferior PCI lanes would be negligible or not. Fairly certain with the p67 two cards in sli one will run in 16x while the second is at 8x.

I've actually been researching this exact situation, as I've got a 3570k on a z68 board and plan on SLI'ing two 1080s later this year. I found someone on Reddit who tested his old 2600k vs. a new 6700k, and found very little difference in performance. I expect the same will hold true in SLI as well. The extra performance of the second card, which will likely be slightly bottlenecked, should still be more than enough to be worth it in my opinion. 
 
the Reddit post, for reference: https://www.reddit.com/r/nvidia/comments/4puyrg/gtx_1080_sandy_bridge_vs_skylake_tested/