Considering the drawbacks of speed-reading (it's not just "reading, but faster") are really counter-productive in programming, I don't think actual speed-reading techniques are helpful when reading code.

I certainly do find myself "skimming" code in larger code bases but then I'm also not speed-reading but simply looking at the visual structure (which is where consistent formatting matters) and looking at words in fixed locations (e.g. names in function definitions).

When you actually have to read code (rather than just skim it by looking at structure and words in fixed locations) that usually means you need to focus and carefully follow each expression -- the bottleneck in this case is comprehension, not reading speed (unless you have to keep track of each character, such as when dealing with short and confusing variable names or intentionally obfuscated code).

We read code in order to understand it, and I believe one must read code with whatever technique that lets them understand it best (I know nothing of this subvocalizing thing; I came here to see what it was). For me, reading code is a deliberate activity, in that one must spend some time with it and not whiz past it. Further, speed reading seems irrelevant, not to mention counter productive, when dealing with code.

I visualize graphs sometimes or draw them on paper for particularly tricky pieces of code.

I was subvocalizing things to remember to do before learning to use task tracking software for that.

You might want to benchmark yourself e.g. with http://www.readingsoft.com/ (I ranked 398 wpm and I know my bottleneck is eye movements)

Also I think code reading speed is only a part of a larger process (e.g. code review or making a fix). For both of these external tools are available making reading speed not as important (iterative development / unit tests for fixing + static code analysis tools for reviews)

I'm not conscious of doing so, though I often subvocalize when reading. You can try humming (vibrating/pulsing the voice box area) or listening to brainwave entrainment audio to lower the amount of subvocalization. Brainwave entrainment audio should also help you better concentrate/focus and relax.

By the strict definition of subvocalize, definitely yes. I don't move my lips, though. Also, it's nothing at all like reading English. I'm trained to read logic directly as logic.

Interesting question. With code I don't unless it's 'complex' and I'm trying to work something out and I just realised I don't with music either, but I definitely wouldn't consider myself a speed reader either.