All depends on how much revs you'll see and how close your engine is to detonation. Stock Ford spec stuff will last a long time on even a 150 hp, and its only past that where extra insurance is needed.
In the USA, you've got three step up choices...stock Sliverlite pistons in flat top Tempo 2.3 or tall deck 8 cc 4.2 (255) V8 to 200 hp, then go to aftermarket new old stock 12 to 6.5 cc TRW's forged pistons from 250 to 450 hp, then get some custom Ross/Wiseco forged after about 450 hp
As long as the clearnace is right and the ring gaps suit the rev range, and you don't have a suspect cast alloy aftermarket piston with slotted compression groves at the top of the piston, you should be okay to about 200 to 250 hp with Ford cast pistons. There have been a two noted failures with the Tempo HSC 2.3 piston, but our I6 engines are often set up with stock clearnances for rings and pistons, and there is evidence from other 200 cube engines that the stock Ford figures are not ideal for performance engines which see upwards of 5000 rpm often.
If you change to what we called overseas (Australian) Duralite cast alloy pistons (15 to 27 cc dish), or better still, change to Mahle based coated cast alloy pistons like ACL or ACL Race (4.5 cc dish) , you can see up to 450 hp. After that, we then go to a forged TRW/Sealed Power/Ross/Wiseco.
What people are finding is that forged pistons are likely to be set up incorrectly for clearnance due to a lack of information on when ring flutter starts. So if you have a piston clearanced for 5000 rpm, then it'll destroy the bore or piston at 6500 rpm. A cast alloy piston won't take over-reving for long.
