What is a "carbide pin"? Did you mean endmill?
As far as carbide on aluminum with a lower RPM spindle such as you have, your only REAL advantage is going to be less tool flex with carbide. HSS tools can flex quite a bit and leave scallops that carbide will be much less likely to leave.
As far as steel and stainless, carbide is highly reccomended. Carbide has higher working temps and less flex which will allow you to increase your feeds/speeds, DOC and axial step over, as well as IPT. Even with a 3600 RPM spindle, you'll see night and day differances on steel and SS.