Two 150 GB Raptors in RAID 0 is definately going to be fast.
The X version is noiser, so you might want to get the non-Windowed Version instead.
---
People tend to vastly overestimate the number of activities in which the hard drive forms a bottleneck.
Rather than guess or listen to other people guess, its best to search the web for some hard numbers.
If you see benchmarks showing Raptors beat 7200 drives in the types of photoshop operations you will be doing then go for the Raptor.
If you see benchmarks showing RAID-0 beating single drives in the types of photoshop operations you will be doing then go for two RAID-0 Raptors.
--
If you simply want to know (or brag) you have the fastest hard drive setup possible then forget about the benchmarks and buy the Raptors.
--
Make a small partition at the begining of the drive for your OS & Software. This is the fastes section of the hard drive and it will ensure maximum performance for you C: partition as well as help you keep your software and data seperate.
---
Given that you will have 300 GB of storage that has double the normal changes of failing, use backup software to automatically protect anything important.
Save the images to another hard drive and move them to DVD/external hard drive as often as you feel is necessary given the importance of the data.
--
PS post links to any good benchmarks you find.