If the toys you speak of are Native Sample Playback apps. you'll need SSD's.
For example Kontakt only needs SATA III SSD's and a 20k DFD setting, over riding Kontakts' 6k default setting. Most guys use 12-16k for DFD but they don't own an XITE-1, we do, so 20k and SATA III SSD's work fine.
If you are using VSL or PLAY sample playback apps, they can still work on a more limited basis using SATA III SSD's.
I just did finish a new Supermicro build with their 1U 14" deep chassis, and their new Z97 1150 motherboard.
It has a built in M.2 PCI-e connector on the motherboard, which is 4GBps faster than SATA III, and directly connects to the i7 4970k CPU. The specs are not real wolrd though, but break down like this, SATA III 6GBps equates to 515MBps in seq. read rates, and 80k random reads. More than enough for Kontakt, and I use 12 x Instrument Banks each with 16 instruments, spanned over 12 MIDI channels.
PLAY and VSL still gag using SATA III, but on the new M.2 PCI-e @ 10GBps, I get 760MBps reads and 110k Random IOps. So I use the Samsung XP941 for all samples, then have old SATA III SSD (OCZ Vector 4) for the OS+Apps.
Gary is right about all new designs working fine for x64, but it's the streaming from disk x64 apps that are picky and need fine tuning and new hardware for real time use.
http://impactsoundworks.com/optimizing- ... ow-part-3/
Here's some really well documented tips for Kontakt from a top shelf developer which will really help if you want to just stay with SATA III.
For PLAY and VSL, little is documented on their performance except for whiny guys crying about streaming troubles, and even when I tell them they need x-amount of IOps and higher seq. read rates they still piss and moan about bending over to pick up another dime for hardware. The developers sure don't tell people how sloppy their code is, but it's really easy, over come sloppy code with brute force.
I'd be happy to help on a parts list if you need, but most folks just stay with Kontakt as there are excellent developers with great Orchestral libraries, negating the need for costlier massively obese PLAY and VSL 500 mic positioned instruments.