Every machine has a raid 1 of "high performance" SSDs. Most have Corsair force3 GTs. The 4th gen is an untrabook with room for only one SATA3 ssd, so I put a Mushkin M3 drive in in for the raid. The Newest machine some other SSD that is just slightly faster. The read speeds are something like this 1st gen -> 1.2GB/s, 2nd gen -> 1.2GB/s, 4th gen -> 1.1GB/s (the M3 drive slows it slightly), 6th gen -> 1.3GB/s.
Each machine is faster than the previous by a wide margin, far more than the proportional speed difference from the slowest to the fastest. There is almost a whole minute between (3m to 2m) from the 4th to 6th.
The first gen has 2 cores with hyperthreading (looks like 4 in gnome system monitor), the quad cores with hyperthreading where far out of my price range. All the rest, the 2nd, 4th and 6th gen have 4 cores and hyperthreading (looks like 8 in gnome system monitor).
For reference each of these was around $1,600 plus or minus $200, except the 6th gen. The 6th also has an nVidia 980 (not the normal mobile version) and 4 total hard drives. The other two drives are large mechanical disks that I only mount when I am doing stuff with movies or other large offline data, I do not believe they have any impact on the benchmark. This machine cost $3,200 after all the crap I did to it.