That startech one isnt going to be too good, but since you need low profile its probably about as good as you can get.
As for the 5570, it doesnt really matter who you buy it from since you arent going to need higher end components and cooler to give you a great OC, but i would still stay clear of powercooler and go for the cheapest low profile one. I wouldnt get one with passive cooling, it requires your case have good airflow to keep it cool, something prebuilts are not known for, the active cooling fan shouldnt be loud enough to matter.