Pretty sure that the tti's make more power than schu's. But the schu's have a lot more ground clearance. Schu's are easier to install too. Way easier. I remember reading somewhere that on a 500hp motor the schu's were down about 40hp from Hooker fenderwells. If that helps.
If you go with the TTI's get the 1-3/4" primaries. My 2" primaries are overkill. Plus you have more room for those tight spots. I have Schu's too but they need to be modified for 4 speed cars.
you'd better check out some facts first. A tri -y design is better than you think
The Schu site does show a decrease in power compared to full length headers. It doesn't show an improvement compared to manifolds. There are cars in F.A.S.T. that run in the 10s through manifolds with skinny bias tires. Headers are definitely a preference thing. There are compromises to headers and manifolds. To me, the manifolds win out.