New generation of Exadata was announced last month.
Exadata Database Machine X5-2 | Oracle
Accelerate performance for all workloads by up to 10x
Now with Database In-Memory, DB node's CPU and memory specs more directly influences DB performance.
The article below compares the very models of Xeons which are used in X4 and X5.
Intel Ups Performance Ante With 'Haswell' Xeon E5 Chips
12-core Xeon E5-2697 v2 against an 18-core E5-2699 v3, software makers are seeing anywhere from 20 to 90 percent improvement.
Improvement in Database In-Memory going from X4 to X5 "depends" on many factors.
One of the DBIM characteristic on CPU usage is SIMD instruction. i.e.) AVX, AVX2.
The blog below by famed Oracle expert has info about X5 and SIMD. This is non-Oracle site and I can't comment about the accuracy.
Oracle In-Memory Column Store Internals – Part 1 – Which SIMD extensions are getting used? | Tanel Poder's Performance & Troubleshooting blog
X4 in the lab wouldn’t have helped with finding a CPU with AVX2 – the X4 doesn’t have that. But the new Intel E5 v3 chips that will be in the X5 do
I googled for SIMD benchmark of sort but could not find it. I don't thin Linpack fits. Even if I can, I wouldn't rely too much on it.