Going with multiple drives is the best way to go...partitions are not usually advised. I'm sure someine here with a more technical base can explain why this is, but I have read on here from Sonar 4 and on that partitions are a headache...just my 1 red cent...
The issue is head movement, the electromagnets that read and write to the hard drive must move across the spinning platters on a pivot arm to get to the location to read or write. That physical problem is the bottleneck on read/write speed. The advantage of multiple drives is that the heads on each drive can be moving simultaneously which in conjunction with the cache allows much faster access. Putting everything on a single drive means you can only generally be reading at one point at a time, and the heads have to re-position to move to a new segment of data. The distance that the heads have to travel to get to the next sector is a minor but significant factor in keeping the data flowing. If you put data on different partitions, then in the event that sequential reads are on different partitions, you will probably make it necessary for the heads to move further (across a physical partition boundary) to get data on a different partition. A single partition might (but will not necessarily) involve shorter distance of travel. Partitions may (but will not necessarily) slow access, but separate physical drives will almost certainly speed up access. It is possible to set up partitions that improve access by putting the critical frequently used data on the fastest part of the drive.
Partitions are not a pain in the ass, or particularly problematic if you use them properly. I always partition my system drive since large drives have a huge excess of capacity over what is needed for most OS and program storage. I create a small tight system partition that is easily backed up with an imaging program, and use the excess space, on a second partition, for backups etc. I am not aware that a partitioned drive is more prone to failure or more difficult to recover data from after a crash. In some cases they may be less so. The hidden recovery partition under Windows is a testament to the utility of protecting data by partitioning.