go for the aftermarket. but if your in a pinch, use your stock cooler, dont Overclock, and put your 21 dollars into a special place and toss your chump change into it till you can afford something a little bigger. Im running a heatsink like the one you show, it just has 4 heat pipes and a 90mm fan. and its cooling a q9400 o/c to 3.2GHz really nicely. it only cost me about $45 total.
BUT if you have no choice, im sure that little 2 heat pipe 80mm fan will out preform the stock cooler by at least 10 degrees on load. give or take depending on room temp and case circulation.
What are your ambient temps? 70 seems a little high even for the stock. OFC every CPU is different but mine runs at 29C idle and 55C load and thats with an overclock to 3GHz. At stock it was 28C idle 50C load. This is all with the stock cooler and ambient of probably around 20C. VCore is 1.25 on the overclock - and the VID(?) for the chip was 1.325 so not a great start point. Maybe I just got lucky and have a cool chip and a good transfer between CPU and heat sink. Certainly heat has not stopped the overclock, I just haven't managed to get it stable at 400FSB yet - although to be fair I haven't really tried that hard as 3GHz suits me..
The stock heatsink for the Q6600 is twice as large as the heatsinks that come with the 45 nm Core2's. Unless your ambient temps are abnormally high or your case has poor airflow through it, you should be able to use the stock HSF at 3.0 GHz.
Many Q6600's will run at 3.0 GHz without any increase in vcore.