I have max 2 risers connected this way and it works fine. GPU will of course have their own dedicated connectors. Connecting all 4 risers to the same cable maybe a bit overkill. You should have plenty spare cable and slots with the GPU though. Take a look at the discussion in this post for some details:
PCI Riser Power Test, Results, and RecommendationsEdit: You may want to move this topic to the Altcoin mining board as topic relates to GPU mining:
https://bitcointalk.org/index.php?board=160.0. The link will be at your bottom left to move topic/ lock topic