Reading speed when dealing with a combination of quick tempi and complex music is not solely about reading ahead. When we need our reading to keep up with the pace of the music, we also need to change the way we read.
For example: say you had a figure that repeats a lot, like in opera accompaniment where something could repeat for 16 bars, 24 bars or longer. Do you attempt to read each one of those 16 bars to get ahead? No, you don't have to re-read something that does not change. Read the first bar, count the repetitions, then move on to reading what comes next while your hands play on.
Another thing to do is read using abstraction layers. You don't need to start playing with 100% resolution. You can approximate the music, and every time you make another pass you add detail to the stuff you already know about the passage. This way you are able to get the essential elements of the music in your hands and ears quickly, then over time add detail to that basic structure. You end up with usable music much sooner, rather than a whole bunch of parts which you know very well yet still need assembly.
I can relate to your situation, as memorization came very easily to me but I needed to study how to read effectively. For a process workflow I would use something like:
1) Memorize:
1.1 - sight reading
1.2 - analysis
1.3 - fingering / technical problems
1.4 - musical problems
1.5 - interpretive considerations
1.6 - critical listening
2) Listen, be attentive and revise. Refer to step 1.
Memorization is not a separate section of the learning workflow, but rather the workflow is designed for memorization efficiency. One memorizes as one works. By the time one has done the bulk of the work, the music is for the most part memorized.