Great looking boat and welcome too the Supra family. I bought my 2006 Supra 21v last year. The previous owner had already upgraded the rear bags to 750s and the center bag to a 1250. I also bought another 400b bag to place on the surf side seats. I would fill the surf side rear bag full, non surf side about 50% and center bag full, 400lb bag full sitting on the surf side seats and have everyone sit on the surf side. As for speed it was usually around 10.5 mph. It created a surf able wave, but do to the swim platform having a huge lip on it there was a lot of white wash. Not only that, but I hated having to ask people to move just to get a decent wave. Again the wave was not the best but surf able. I just recently added the GoSurfAssist tabs to the boat and also a new Supra surf swim platform. The outcome is a night and day difference. No more slamming one side of the boat. If there is just a couple people in the boat I just fill the two rear 750s full and center full and hit the surf left button and done. I will say that the GoSurfAssist system and new platform isn't cheap, but it will produce the best wave you will ever see on a 21v.

Here is a picture of the wave before the GoSurfAssist and new swim platform install. Notice all the white wash. This was about average of what the wave looked like depending on water depth weight placement.

And here is a picture of the wave with the new upgrades. This picture is with both rear 750s full and center 1250 full. Two adults in the boat and we are running around 10.5 mph.