Is it possible to install 2 500gb sdd's into a 2012 iMac?

The Fusion Drive is a combination of and SSD and either a 1 TB or 3 TB HDD depending on the iMac model. The SSD does the startup and speed-loading functions, the HDD does the mass storage functions. Makes a very fast system from what users with that configuration say.

Sincee the HDD is on the eSATA bus as is the SSD, you get the fastest possible response. But you can get fast response by having the internal SSD (the 768) and a Thunderbolt external HDD. The eSATA runs at a sustained 3.2 Gb/sec transfer rate, the Thunderbolt has a theoretical upper limit of 10 Gb/sec. So, in theory, the TBolt could be faster, but you are still on a different logic board bus so have that issue to deal with on actual transfer rate.

Did the Apple tech support person say to use that external SSD as the boot drive and the second part of it as RAID, and the internal for BootCamp? Seems a little strange to not use the internal partitioned for normal boot and BootCamp and then the external as a bootable and RAID, but eitehr way should be really fast...you are using all SSD technology on fast buses.

Interesting approach - if you buy and setup that system test it booting both ways and see if there is a measurable difference - would be curious to see the results.