Googling should yield HDTach throughput numbers for the configurations you are considering, but game loading time will be very difficult to find.
Unfortunately you will find an increase hard drive throughput is going to give you a smaller than expected decrease in loading times.
Typically the majority of game loading time is spent processing the data after it is read from the hard drives.
Compare a single 750 GB Seagate to two of them in RAID 0. The sustained transfer rate jumps to 130.4 MBps but the level loading times are not that impressive. If you expect games to load twice as fast you in for a disappointment.
You will gain performance, but RAID0 doesn't scale as well as you think. After 2 hard drives the performance drastically slows down. I have 2x74GB Raptors in RAID0 and get a solid read of 100MB/sec. Writes are about 95MB/sec or so. My guess is that it wouldn't be worth the money. When it comes to loading games, the hard drives are not really the limiting factor. Granted, data is loaded from the hard drive, but most of the time is the CPU decompressing the map or files. It would be better to upgrade CPU and memory to decrease load times, than hard drives. The dual 36's should be able to keep up with the CPU. Here is a benchmark of 2x74GB's. Not sure what speeds you are getting with the dual 36's.
Just to add a few notes to this, my motherboard is a Gigabyte GAK8NXP-Pro. This has a Silicon Image Raid 5 SATA-I controller and an nVidia SATA-II controller.
Due to problems with the design of this motherboard and other Gigabyte nForce4 motherboards, it is impossible for me to boot from the SATA-II controller, the latest drivers do not help - I have tried using them with a fresh install of XP and they crash the PC on first boot, just as the ones which came with the motherboard do. I am forced therefore to use the SATA-I controller for whichever disk(s) I boot from.
The raptors are attached to the SATA-I controller. They would gain little from being attached to the SATA-II controller, except for the fact that it wouldn't be a software RAID controller.
The Seagate is attached to the SATA-II controller as it still works in Windows, although it won't allow drives to be booted from when they're connected to it. I figured I would do this to use the PCI-e bus rather than the PCI bus, which is already used by my wireless LAN, sound card and wired LAN.
I don't think I would recommend anyone else to buy these raptors, I don't think that we home users see the greatest benefit of their fast access times.
Ideally I'd build a new system, keep the 2 Raptors for XP and games and have 3 or more barracudas in RAID0 for overflow. I don't believe in RAID0+1, I think that you either back up properly (onto 2 media, 1 offsite) or you don't. Why entrust your data to something that spends most of its life at 7200RPM?
3 RAID0 barracuda would have the same maximum transfer speed as the 2 raptors, but raptors are faster in access times. Remember that a RAID access time will be equal to the slowest access time in the array and any RAID configuration won't reduce it, on the contrary it will slow down a bit.