Using 750 as your trigger level would give you 10 trades. Most of which are fairly recent. Now let’s use the percentage instead and see what the results look like:
18 trades instead of 10 and results are not as good as they appeared with the first test. Many more instances are found here when looking back to the 70's and 80's. By using raw numbers instead of normalizing them, you’d be missing out on almost half the pertinent data.