most developers don't understand the concept of I/O. The I/O speed is really important in terms of TTFB. Most websites are hosted on SATA drives which have poor IO speed. Even if they are on RAID-10. The speed of CPU doesn't really matter here, unless your app does heavy CPU processing. To speed up TTFB, only thing you can do is to cache/cache/cache, and possibly having a varnish in front of your web apps. Also you'll see substantial boost in TTFB times if you switch over to something like RAID-10 SAS, and even more so if you switch to the newer drives like the SSD. I've seen Magento stores go from several seconds per load to almost varnish-cache level when placed on PCI-Express SSDs.