They will perform the same as far as IOPS and Response time assuming the same number of spindles and the same dataset size/workload.  The challenge with larger drives is that they allow for more data per spindle which can increase drive contention if you consolidate data onto fewer spindles. Some people will short stroke larger drives (use only part of the total capacity) to keep the performance level of smaller drives, but then you have space on the disk that you paid for and cannot use which is not great as far as budgets go.
All:  If both the F146 (fibre channel, 146 GB, usseable 133 GB) and the F300 (fibre channel, 300 GB, useable 268 GB), are both 15K RPM and 4 Gb/s, don't they both have the same performance?  Now, I understand that in the Oracle, SQL-Server and Exchange worlds, they calculate 180 IOPs for a 15K RPM FC 4 Gb/s drive, so that you get more drives in a file system if the drives are smaller, which increases the IOPs.  So the Oracle DBAs like that.  But, if I use the same number of drives (I will have more "wasted" space on the F300s than I do on the F146s.), shouldn't the performance be the same?     Stuart 
Is an F146 any faster than an F300 (both 15K RPM, 4 Gb/s)?