72c core temp is okay under Linpack load, depending on your ambient temps.
Prime95 will likely run 10c (or more) cooler than linpack... so it really should be fine.
In my experience people tend to over estimate how much radiator is required, but we need to keep in mind there are 3 major factors at play here (yes there are others, tube size, cpu block etc).
1. Rad Size
2. Fan Speed
3. Ambient Temp
It IS possible to have a small rad with high speed fan and get better air/water delta than with a large rad and low speed fans. Hence talking about rad size by itself, is not always useful. Of course, we are on the SPCR forums, so we can make some assumptions about fan speed... but we are still talking a (n approx, depends on rad obviously) range of 200w -> 500w dissipated (at 10c delta, triple rad) with fans between 600 and 1500 rpm.
So, a single rad (assuming linear scaling), with 1500 rpm fans, can manage about 500/3 (170-ish) watts at a 10c delta, which is enough for an i7... at least one that isn't overclocked. OTOH a triple rad can dissipate more heat, with 600 rpm fans, which should be quieter.
I also mention ambient temp. As someone that currently lives in a hot climate, it has always frustrated me a little when people post temps without mentioning ambient temps (I apologise if I missed it in this thread, this is a general rant!). Comparing my CPU temps when my a/c is struggling to maintain 28c ambients, to someone with 15c ambients.... is just not gonna work!
EDIT: Oops forgot to say, my figures are based on skinee's reviews... if you don't know about them, you should!: