Could some one please explain why I get the same disk transfer rate when
running 2 750GB seagae drives in raid 0 as I do running 1 2.5TB single drive.
In HDtach the raid 0 array is almosr double the average read speed of the sing drive.
I also disabled write caching just to see if it would have an affect, but it didn't.
I've posted my wie

We've had this discussion before, here. I would suggest running "winsat disk -v" on both machines and compare output after reading the entirety of that thread and you'll probably find out why they're scoring the same. Benchmarking tools like HDTach are great for measuring synthetic benchmarks, whereas the winsat tests really beat on the drives in very specific ways, and would technically be more accurate in "real world" Windows performance on the device.

Its only one system, I first build it with the one 1.5TB drive. Then I thought that a RAID would be faster
so I bought the 2 750GB drives for the RAID and was going to use the single drive for backup.
I was surprised when thy both got the same score. I did run the winsat command on the raid array
and saved a picture using the clipping tool. Later I'll install to the single drive and compare the output.
I'm sick of reinstalling all my stuff right now so It may be awhile.
Guess I should have just used 2 drives one for my windows install and one for backup.
But now I'm curious about what kind of drive or controller I would have to install
to bring the score up. Adnd would it be worth it.

Worth it? At 5.9, probably not. And the RAID really isn't going to give you much benefit unless you're copying larger numbers of files to or from the drive frequently, and even then the benefits may be marginal over a single drive. Unless this is a volume that's going to store a large number of multimedia files or large archives (like ISOs, perhaps) and will get frequently accessed, your best bet with desktop RAID is redundancy, not speed (RAID1 vs RAID0 or RAID10).