Promise Raid ATA 100

Can I increase performance by adding a 3rd hard drive to my raid array? It is a Promise ATA 100 TX2

I saw somewhere it will add to minimum performace

What, add a third drive so you've got a 3 drive RAID 0 array?
Sure you can, although performance increase I believe as you say isn't that much.
Also remember that you are adding yet a third point of failure for the potential loss of all data!