You want the lowest seek time combined with the highest transfer rate you can afford. Spindle speed has an inverse relationship with seek times and a positive relationship with transfer rates. Just understand that transfer rates do not grow linearly with spindle speeds, as once you've reached 10k RPM or higher, manufacturers use smaller disk platters, resulting in lower areal densities and lower transfer rates at a given spindle speed (i.e. if you spin a 15k RPM drive at 7.2k RPM, it will likely transfer contiguous data less fast than a same-generation native 7.2k RPM drive). If they used the larger platters they'd have too many drives fail due to heat and vibration, not to mention have to pay a penalty in longer seek times.
So as someone who games with 15k RPM SCSI drives, yes, it is much better than 7.2k RPM ATA units. Even the 10k RPM ATA units are much nicer than 7.2k RPM units.