It seems like everyone always says that they don't care if it takes a long time to cut. The problem is, is that if you want the best tool life, you need to cut as fast as possible. You'll need to determine the max speed through trial and error, but you should try and cut as fast as you can, and still get an acceptable finish. Cut quality should be the main factor in determining your top speed. Most home built machines are limited due to spindle power, but the workaround for that is to take shallower passes, at higher speeds. It's also important for tool life, that you clean out the chips between passes, so the tool isn't re-cutting the chips you already cut on the previous cut. Cutting through a cut already packed with chips causes a lot of heat, which is the main factor in tools getting dull. You're best bet is probably upcut spiral solid carbide. Also, you may want to leave a little extra material, and use a very sharp new bit for a finishing pass. But you need to be careful, as it can be easy to get tearout when doing a finishing pass in solid wood.
As for spindle speeds, find a tool from Onsrud's catalog that's comparable to what you're using, and use their chip load charts to get you in the ballpark.