have not found a reason to add a 7th plate, this includes cars that are putting down 450+whp. There is more than enough to work with using the stock 6 clutch setup. I have torn apart a few builds that other guys have modified to add a 7th plate and they were all badly coned and burnt up and these were cars running 12s and 13s. I contacted Alto back in 2001 about a 7 clutch setup for 2nd in the 4T65E and they told me there wasnt really a concern or demand for it and 3rd was what seemed to be the weak point. The link that you supplied shows a PowerPack for 2nd for a 440T4/4T60E which is a completely different clutch setup. I have used several of those setups in 440T4/4T60E High Perf rebuilds and they work great, but again not needed in the 4T65E. If you had a GM Hydramatic technicians guide you would be able to see the hydraulic schematics for each gear and where the fluid goes and there are also descriptions of why the fluid channels where it does. That is the easiest and best way to understand the functions of the holes, though they dont go into detail on the WHYS of the hole size but it does show where the restrictions-holes in the spacer plate are. A good understanding of how it works and why really helps out here and without writing a book on this lol there isnt a short easy answer other than the hole sizes restrict fluid flow not only for shift feel and timing but also for release. On a production vehicle you dont want full-on volume and pressure reaching the clutch packs or there will not be smooth shift feel so restrictions are put in place to tame things down. What power levels are you at and how fast do you plan to run at the track? I use a direct relation between that and the hole sizes I use, it is not a one-size-fits-all equation
