well, in a radiator, you have the water flowing through a section of tubing which stretched across the radiator, whereas a heatercore the water in distributed through hundreds on small fins which cover more surface areas...therefore thermal dissipation on a heatercore will be greater than that of a radiator
I'd say the heatercore would perform better, and like I said, much cheaper as well, plus no doubt you're adding a lot of resistance to your water loop
The mod is very easy to accomplish, it was the first time I've done anything like it and it went off easily, Nubius who is also a member also did the same mod for the first time at about the same time as me
There's mine, it took me about an hour to do and I didn't feel like I was struggling with the mod at any point while I did it
If you still don't feel comfortable doing it yourself, head over to xtremesystems.org and find a guy named "weapon", for about $80 he'll mod the heatercore for you and throw in a shroud and a nice paint job...I was originally going to buy one from him until I located the guide to doing the same mod yourself and decided to save my money and do it myself