I just took delivery of a 2004 353 with hp 500's no boxes. The props on the boat which the seller said were original are bravo 4 blades but they are stamped 31 pitch turning out. It is obvious the blades were worked some as they are thinner than stock bravo ones and I don't believe you can get a stock 31p (I understand Formula ships boats with labbed props?) I can run 5200 rpm's very light on fuel and 4900 to 5000 with a decent fuel load. Speedo reads 80 mph at 5000 ish rpm which equates to 17% slippage (assuming gaffrig speedo is anywhere near accurate)
Question: Who has tried spinning props in on a 353 with stock power and what are your results? (just interested in speed gains and planing not docking)

nobody has honest test results turning in?

We had a boat a couple of years ago we turn the props inward on and lost the mid-range pull that we were use to at 50-70 mph. call Formula and talked with some of my friends up there and they told me they did not advise turning props in-wards because of the running attiude the curve step bottom had on the 353. It sounds like you are right in the rpm range you should be running if you want to turn 5200 rpm, my advice would to locate a pair of 4 blade Lab finished 30`s to try and see how you would like the performance on those........my 2 cents worth on it......Capt. Steve