It isn't that I'm afraid of it, but more that I don't know what numbers to plug in...
I haven't chosen the exact heater core I'll be using yet, just that it will be the biggest that I can find which will fit in an 11" tall by 8" wide space... I thought I had a pretty good idea, but I was recently thrown for a possible loop when someone said that the sizes in the HC database were just for the cooling surfaces, and didn't include the tanks. (Is that true?, if so, how does one guess at the overall size given the cooling surface size?)
Beyond the idea that they'll be the quietest 120mm fans I can find with decent airflow, I haven't picked the fans either. (come to think of it, I might even see if there is a bigger fan I can use...)
0bviously if I'm unsure of the exact hardware, I won't have exact numbers for it. However I feel comfortable in saying that what I'll choose will give me average or better results, just don't know how to calculate them exactly.
However, between BB2K's 1/4 degree estimate, and Les' graph posting of the Chevette core showing only a 4* rise with really bad airflow, going rapidly to under 1* as the airflow goes up, I think my 1-2* assumption is pretty safe. For my purposes, I don't need 'Joe Grade Accuracy' (TM)

just a ball park number.
Thanks again for the help...
Gooserider