It really depends on your development goals. I'm not certain if Windows CE 5.0 is a "supported" target (I'm actually pretty sure it isn't) for Studio '08, though I've used it for managed code successfully. This is like CE 4.2 and Studio '05. It's not supported, but it works for managed code if you deploy the framework manually.
I've not tried the native debugger from '08 against a CE 5.0 device. I'd suggest using the eval version on another machine to test before committing.