Quick question, I know forged is stronger in performance applications but cast is more streetable with mild performance.... Will flat top cast pistons be able to handle 400 to 450 hp with between 9:8:1 up to 10:5:1 compression and occasional jumping on the throttle.... I also know forged expand so they dont fit as tight in the bore during normal driving

 

HP and compression are not the main factors when choosing between cast and forged pistons, the engines intended purpose and max rpm are important when choosing piston types. A race engine designed to spend most of it's time in it's upper rpm range or is reved more than 6000 rpm need good forged pistons.
DD or mild street engines that see the occasional romp but stay under 6000 rpm will do fine with cast pistons.
Forged is just as steerable as cast, they just cost more and can take more abuse.
.0045 is recommended clearance for cast pistons.
.006 is recommended clearance for forged pistons in a street engine.
That's only .0015 difference.
If your not planning to rev more than 5500 to 6000 on occasion cast will be ok.
If you plan to wring it's tail and push it into the 6000 rpm plus range deffently go with forged.

Years ago I helped a buddy build a budget 427 for his SS Chevelle, we used Speed A Motive 12:1 cast pistons, a ring broke after three years of DD and the occasional trip to our local drag strip but the cast pistons held up ok, at the track he shifted at 5800 rpm.

 

The engine is going to be a 390 ford .... Quick question, what do you mean by DD, .... The truck won't be drag raced any but I will definitely jump on it every now and then at a light lol

 

DD = Daily Driver

I'm quite familiar with the 390FE engine, owned a few, worked on several.
I have the larger bore 406 waiting to go in my Fairlane.
My nephew has a 390 in his 78 F-150 4x4 and a 427 in his 64 Galaxie.
Both have forged pistons, he turns the 390 to 7500 rpm when he sled pulls.
Street stock class of course, it's only a F-150. he he he

 

If you have the money, go forged.
If you don't, and the car is going to see the duties you described, cast will be just fine.

One benefit of forged, is getting a better, more modern ring pack. Another benefit is failure mode. If a cast piston breaks it shatters, a forged simply deforms. If I was running a very rare block, I would consider that failure mode when building the engine.
Would I tear down an engine *just* to install forged pistons? no.

 

That much HP and comp. get the forged.