Hi Guys, Maybe some of what I've heard about will help you decide, or perhaps confuse things further.
For offroad, the 8.5 (that's the ss5800) in standard form, is better then a nineteen turn. At least from the customers and racers I've spoken with.
For Touring Car, the 8.5 in standard for is better then a 19 turn.
Both situations from what I've heard are very noticably faster.
Now, the 10.5 (that's the ss4300) has been reported to very close to 19 turn for a lot of situations, mostly oval and 4 cells.
With TC guys, For very close competion tracks, the 10.5 may be a tick slower then 19 turn, but way faster then stock.
Now, take the updated SS rotor, put that into either and they both get slightly faster. Actually, the magnet is stronger and more resistant to overheating damage, so you end up gearing up about 1 tooth, sometimes not. Depends on the driver style and car setup, but it's more noticable in 6 cell stuff then 4 cell. Most of the 4 cell guys reported no difference.