That kind of speed up doesn't involve the filesystem. What would help is how you physically connect the drives.
When you connect a disk drive to a controller, only one device can talk to the controller at one time. This is because of the cable connecting them. The wires simply cannot transmit multiple "conversations" at once. So, it never actually gets to the filesystem level; the bottleneck is in the physical connection.
This is why you will see people put their heaviest use drives on separate controllers. Say you want faster virtual memory access. You would put the drive with your swap partition on one controller, and the drive with your data partition on a different controller. As an example, say your memory is full (i.e. you're using swap space), and you launch a new application. The computer can tell the disk with the program to start reading the data, and at the same time, tell the disk with the swap partition to start "paging out" data in memory to make room for the application you just started. Both drives are working in parallel now rather than one at a time if they were connected to the same controller.
Now, your choice of filesystem might have in impact on how long it takes for the drive to read or write data, but the filesystems themselves can't offer multiple, simultaneous access.
For SCSI, you can probably see a problem. Depending on your controller, you can have 15 devices plugged into it. That means they are all competing for the controller's attention. Again, only one conversation can occur over the wire at once. SCSI tends to be faster than IDE for various reasons (mainly raw data transfer speed), but the gap is closing between IDE and SCSI. To my knowledge, SCSI tends to be more efficient in handling traffic, but I'm not that knowledgeable about IDE protocol.
So, what I'm trying to say is this: using SCSI drives won't necessarily speed up your machine. If they do, it would be a comparison similar to upgrading the speed of your processor. Using separate controllers would be comparable to getting a second identical processor instead of a single faster one. Unless SCSI gains you twice the transfer speed of IDE, then it may be more efficient to just move your IDE devices around.
It's not quite
that simple, but it's good enough for government work