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The Increasing Impatience Of The Speed Of The PCI-Express Roadmap
(www.nextplatform.com)
This is a most excellent place for technology news and articles.
No, manufacturers had to redesign their mainboards vor v5, because the frequencies got so high they had to move components closer to the CPU. That and heat dissipation and efficiency issues in first generation, which are still somewhat present on current gen.
At least a few months ago, recommendation for new builds was to go with a v4 mainboard.