Obliviously Exadata X6 will be faster and flexible then the earlier version.Here I have given some comparisons between exadata version with full configuration based on Oracle Documentation.

Metric	X4	X5	X6
CPU	2 Twelve-Core Intel® Xeon® E5-2697 v2 Processors (2.7GHz)	1 or 2 processors with 18 Core Intel® Xeon® processor E5-2600 v3 product family	2x 22-core Xeon E5- 2699 v4 processors
Memory	512 GB Max	768 GB Max DDR4	768 GB Max DDR4
Extreme Flash Capacity	44.8 High Speed Flash	89.6 TB Flash	358.4 TB
High Capacity Flash Drive	168 X 1.2 TB (High Performance)	168 X 8 TB	179.2 TB
Number Of DB Servers	8	8	8
Number Of Storage Servers	14	14	14
Maximum SQL Flash Bandwith	HC:100 GB/s HP:100 GB/s	HC:140 GB/s EF:263 GB/s	HC:301 GB/s EF:350 GB/s
Maximum SQL flash write IOPS	Read:2,660,000 Write:1,960,000	HC Read:4,144,000 HC Write:2,688,000 EF Read:4,144,000 EF Write:4,144,000	HC Read:4,500,000 HC Write:4,144,000 EF Read:4,500,000 EF Write:4,144,000