Ok, if your write solo's that are too fast for humming, SLOW IT DOWN. Who said you had to hum out the idea at the exact speed at which you will be playing it on the guitar. Even when you figure out your own solo's, it's good to first play a fast passage slow so that you can clearly figure out each note. Then play it up to speed when you find the right melodic sequence. If you don't I feel sorry for you, improvising on the spot aside. If you can clearly pull out ideas in your head, you are beyond humming out the ideas to some extent. Even those who can will find humming ideas good for getting ideas out quickly before they leave. If not, there are many ways to get ideas out. Find what works for you, but this is one idea that can help some struggling with writting there own solos. Most novices in this area have the same problem, "what to play next?". I alway tell them to try humming from what they wrote before and see what naturally comes out after. I've never had it not work to some end. Of course explaining it over the internet and not being able to personally explain it is difficult.

All ear training is beneficial since a musician is only as good as his/her ear (inner and outer).