I have a Sofrider and S30, I love them both. I had an opportunity to ride the QX100 last year at the Portland retreat and if you are happy with your SofRider you will really be happy with the QX100. The disc brakes are sweet, I personally like that it still has a shock because I have grown accustom to it and enjoy the soft ride it gives. The tires are slightly wider on the QX100 and I'm not as handy as the guys on this site so I'm not sure if you can still use 1.25" tires on the rims but someone can tell you, if that's important to you in your commute since you mentioned you like the speed. It did feel faster, but to be fair I didn't do an immediate comparison ride on my sofrider after riding the QX100.
I really like the opportunity to outfit the QX100 with packs easily instead of having to do a lot of modifications. If you are into touring that would be a plus. Or maybe you like to haul excess files to and from work ... and need the extra hauling ability ... (you begged us to convince you).
What intrigues me about the QX100 is that it is all new and shiny
and that it appears to be similar to the SofRider but even better.
See, this is the problem.
and it folds,
and the boom adjust SO easily,
and it's even shinier in person, sigh
A miser only makes sensible choices and this is such a sensible choice.