Where he percieves information worth a milennia in a millisecond? That's likely near that level of speed.
That could come out because of his cosmic awareness it could very well not be a thinking speed like you stated.
Also when we are talking it, thinking speed =/= perception speed =/= reacting/combat speed.
Thinking speed = how many thoughts you can process, how many calculations you can perform, how many ideas you can create in your head etc with respect to time. Thinking does not require your body to move.
Perception speed = seeing something moving really really fast, noticing FTL movements, like Supermnan was able to. Being able to process a lot of information per second is different from perceiving light or faster than light movement. Perceiving something fast does imply that neurons in your brain can click and fire and work in way faster than light time frames otherwise the image would not be created in your brain (again depending on who you are perceiving and how fast he/she is going). I think this can be referred from the fight where no one was able to see or perceive Zoom till Flash amped his speed with other speedster then Zoom started to appear as a Blur.
Combat/reaction speeds = These are two of the similar ones. There is a slight different between the two but there are more or less related. Reacting to a certain level of speed like FTL speed attacks is just a level below than performing some movement/ reflex (combat speed) in time frames that light barely moves. Like in the scan Krleavenger posted, light barely moves a millimetre in a picosecond that is a combat speed feat, showing you are moving and reacting in time frames where light would be a statue.