Yes, I'm still using the IG Speeds. My Speeds are a bit heavier than stock. I have leather grips and lead in the hoop. With overgrip and dampener, mine come in at 12.46 oz.
I may have had a poorly strung London demo, but I didn't really like the London when I demoed it. IIRC, it felt way too light. To be honest, I've heard so many good things about the frame, that I've been tempted to give it another shot. But, I was mainly concerned about it getting pushed around since I mainly hit with either college or former college players who can produce a pretty heavy ball consistently.
For me, I know that if I really want to improve, or at least get back to a semblance of my former self, I need to just pick a racquet and stick with it. Switching racquets messes up my strokes. That's why I've been with my Speeds. That said, trying different racquets is so much fun...