It is pretty difficult to answer your question. It depends on what materials you are cutting, type of endmills you are using, type of toolpath, geometry of the part, etc. There will be a learning period while you get used to your new spindle. Here are two resources that are really good for helping you build up the base knowledge that will help you determine the right F&S for any situation:
And this Excel workbook/forum thread:
I did the same upgrade and have loved it. One thing to know is that you are unlikely to break anything more than an endmill if you get your F&S wrong. The shapeoko is very robust and hard to break anything that would be expensive to fix.