I finally got around to testing the ram RAID striping vs concatenation, and by far striping is faster. The supposed bottleneck of using striping seems to not be a problem in these tests, as current CPUs (and Dual memory busses in the G5 at least) seem to be able to handle it quite well with no real significant bottlenecks (at least when using 2 disks in the array. There is a bottleneck if more than 2 are used ). In Xbench 1.3 the disks scored as follows:

Concatenating 2 ram disks (4GB total):
Sequential
Uncached Write == 159.39 MB/sec [4K blocks]
Uncached Write == 663.16 MB/sec [256K blocks]
Uncached Read == 50.68 MB/sec [4K blocks]
Uncached Read == 734.83 MB/sec [256K blocks]
Random 1989.25
Uncached Write == 100.79 MB/sec [4K blocks]
Uncached Write == 586.58 MB/sec [256K blocks]
Uncached Read == 51.45 MB/sec [4K blocks]
Uncached Read == 669.82 MB/sec [256K blocks]

Striping 2 ram disks:
Sequential
Uncached Write == 197.69 MB/sec [4K blocks]
Uncached Write == 667.07 MB/sec [256K blocks]
Uncached Read == 52.49 MB/sec [4K blocks]
Uncached Read == 969.91 MB/sec [256K blocks]
Random 2146.64
Uncached Write == 95.03 MB/sec [4K blocks]
Uncached Write == 748.22 MB/sec [256K blocks]
Uncached Read == 49.81 MB/sec [4K blocks]
Uncached Read == 1035.02 MB/sec [256K blocks]

Interesting results. Anyone else got anything to submit along these lines?