The formula is simple:
the longer the runners on the header the more HP you get, and the more torque you lose.
The Hotshot unit, I have been led to believe, is a shorty header, it should give you good low to midrange power gains, and step up the tourque below 5 grand pretty well.
also there are two types of header 4-1 and 4-2-1
4-1 headers go from four pipes merged straight into one single collector, this type is best for torque gains.
4-2-1 are staged headers, four pipes merge into two, and those two merge into one, this reduces your backpressure a bit and is good for hp gain, but not as good for torque.
the hotshot header for the escort I owned at one pont was a long tube, 4-2-1 header. it flowed really nice, and made nice power from 3K to redline, torque shot up form around 3-5k.
a shorty header with a 4-1 setup will make good power all across the powerband, espescially from 1-5K, and torque will be much improved over stock, especially in the top end of the powerband.
the key is finding a header that has been properly tuned for your specific application. If you need more midrange power and torque, better to go with a hotshot header, but if you need top end power, then going with a full race, long tube 4-2-1 would be good (think trial or Brash Boy header).
Also realize this... a header won't do much unless you have a matched exhaust to flow the extra fumes from your cylinder head. most current cat-backs should do the job. more backpressure for more torque, less for more HP. also, the less restriction you place on your exhaust, the higher in the powerband your gains will be noticable.
if after your header is installed, it feels as if you are losing too much torque, try putting a silencer in your exhaust, or add a resonator upstream (I did this on my escort, the header, hi-flow cat and large exhaust made the car way too loud, and it lost torque. adding a nice, 8" resonator fixed this problem)
hope this helps,