SAS is actually really good, and there will be a difference, but not very much. IMO 7200 > 10000 jump is probably larger than 10000 > 15000, because you also jump to 2.5" disks, which means that you are working with a lot lower stroke length, which also helps.
I was just meaning, with the high cost of the drive plus the card to drive it, the extra cost wouldn't be worth it. I think you can just get a SAS to SATA backplate, but that will cost, although not a lot.
From the wiki article
http://en.wikipedia.org/wiki/Serial_attached_SCSI
Serial Attached SCSI (SAS) is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations, and it uses the standard SCSI command set. SAS offers backwards-compatibility with second-generation SATA drives. SATA 3 Gbit/s drives may be connected to SAS backplanes, but SAS drives may not be connected to SATA backplanes.
Comparison with SATA
Systems identify SATA devices by their port number connected to the host bus adapter, while SAS devices are uniquely identified by their World Wide Name (WWN).
SAS protocol supports multiple initiators in a SAS domain, while SATA has no analogous provision.
Most SAS drives provide tagged command queuing, while most newer SATA drives provide native command queuing, each of which has its pros and cons.
SATA uses the ATA command set; SAS uses the SCSI command set. ATA directly supports only direct-access storage. However SCSI commands may be tunneled through ATA for devices such as CD/DVD drives.
SAS hardware allows multipath I/O to devices while SATA (prior to SATA 3Gb/s) does not. Per specification, SATA 3Gb/s makes use of port multipliers to achieve port expansion. Some port multiplier manufacturers have implemented multipath I/O using port multiplier hardware.
SATA is marketed as a general-purpose successor to parallel ATA and has become common in the consumer market, whereas the more-expensive SAS targets critical server applications.
SAS error-recovery and error-reporting use SCSI commands which have more functionality than the ATA SMART commands used by SATA drives.
SAS uses higher signaling voltages (800–1600 mV TX, 275–1600 mV RX) than SATA (400–600 mV TX, 325–600 mV RX). The higher voltage offers (among other features) the ability to use SAS in server backplanes.
Because of its higher signaling voltages, SAS can use cables up to 10 m (33 ft) long, SATA has a cable-length limit of 1 m (3 ft) or 2 m (6.6 ft) for eSATA.
Hope to help a bit!