Well, I was skimming through video.google.com, looking for some Clone War clips when I fell across this piece:
Anyways, I decided to do some rough estimations (others are free to make their own estimates) and I came up with interesting numbers. I thought it would actually be easier to work my way from inside the battle outwards, as I wouldn't make double counts. Venator Star Destroyers which were the same ships in prior snap shots were labeled R and those which were not were labeled with a number.
After I went through each picture labeling the proper ships, I tallied up all of the ships and came to a count of 28. Then, using some rough proportioning, I slowly worked my way out again until the very final picture which had a picture size of 727 x 510 while the size of the selected green frame was 55 x 40 (with the green frame representing screen 3). Taking the two areas and finding how many of the green frames fitted into the larger picture, I came to a rough estimation of 169.
Assuming that the distribution of Venators is roughly the same as it was in the select frame, I made the following estimations. So, assuming a conservative Venator distribution of 23 per green frame, I came up with a figure of 3864 Venators. Assuming the 28 I found, I came up with a number of 4732. Assuming an upper estimation of 33, I came up with 5577.
Multiplying these figures by the Venator troop capacity (3,900; I couldn't find a source so I relied on wikipedia), I came up with 15 million, 18.4 million, and 21.7 million, respectively.
Using the same method for star fighters (with a compliment of 420 fighters per Venator), I came up with 1.6 million, ~2 million, and 2.3 million respectively.
Given these rough estimations, its clear that several millions of clone troopers were deployed in the naval battle and even several millions more (hundreds of millions at least) were deployed on the ground. Coincidently, this fits perfectly with the 1:50 rule.