depending on the CPU and the graphics card and the temperatures you want you may want to consider more than just adding a 120mm rad in for the GPU.
I'm looking to run a 360mm Black Ice SR-1 rad and a single 120mm EK Rad (not impressed by the EK rads, but it's the only 120mm rad I have lying around) to do my Phenom II and GTX 480, but to be honest I'd really want more than that if I could. I'm currently running a 240mm XSPC RS240mm Rad and an EK 240mm Rad (I bought the EK rads believing them to be good because they were made by EK!) and they struggle with my Phenom II and 4870x2 unless I have my Akasa Viper Radiator fans running at 1200-1400rpm. Running at that speed they are LOUD and the temps are acceptable (possibly even quite good, hard to find Phenom II X6 temps to compare to).
I would go for the HF kit over the LT kit though, for the CPU block if nothing else. The better pump is just a bonus (even if it is louder). I'd say go for as much radiator space as you can fit in your case though really. If you try to do it too cheap you may be disappointed with the results or have to spend more money (like I did) trying to improve it later.