How long should a spiral bit last?

[ttw06]

I know this questions depends on a lot of variables, but I was curious to see what other peoples experiences were. I cut a lot of 3/4" profiles in oak, walnut, and melamine, and it seems like I buy spiral bits constantly. I use a feed rate of 75 in/min with a cut depth of .22 in. I also use solid carbide bits. I would appretiate any suggestions for feed rate, depth of cut, brand of bit, or any comments you have. Thanks