The LSI U160 in a standard 32-bit/33MHz PCI slot has a limit of ~127MB/sec assuming the PCI bus isn't doing anything else at the time. The Atlas 15k II peaks near 100MB/sec (averaging around 85 MB/s) - a second one and you might saturate the PCI and/or the U160 bus, but of course it will still work, just not as fast as it could. You really need a server mobo with a 64-bit and/or 66Mhz Extended PCI slot and a U320 adapter to get the best from multiple drives of that level - they aren't really made for personal use.
. IMO, some of the latest generation of 10k SCSI drives will do best with the U160 adapter on a standard mobo while saving a bunch of bucks... But the OP just wants to use the one 15k drive and for that, the LSI U160 will do fine.
.bh.