An 8x6 would almost certainly give you better straight line speed. BUT, when you pull that high-G turn, you'll bleed almost all your speed away. You won't be able to hold the elevator and loop until you don't feel like looping anymore either, and you won't have the climb rate. I can put my P-47 in to a nearly vertical bank, pull full up elevator, and stay there, turning very very tightly. With an 8x6, you'd bleed speed and fall out of the turn eventually.

So, if I was flying against, you, you might go roaring past at warp speed, but you have to turn sooner or later. So I'll wait for you at the end of the box, and jump you there. If, somehow, you got behind me, I'd either climb vertically, or just start looping or do a tight climbing spiral, knowing that eventually you'll fall off, and I can reverse and drop on you for an easy kill. You'd be forced to dive away from me, and hope you accelerate before I get a line on you.

It's combat, not pylon