Alright - looks like the X5670 and X5675 are going for between 100 and 125, which seems real reasonable, so I'll probably just order a brand new X5675 for $125 off eBay. Next problem is that there is currently a stock intel cooler in the PC.
It seems like the popular coolers on the forum are Scythe Mugen/Kotetsu, Noctua NH-D14, and AIO liquid coolers. Ppl with Scythe coolers - are you getting good temps, or is the premium on the Noctua worth it?
The Kotetsu is a remarkable little cooler. For stock or mild overclocks. It won't do well beyond 3.8/1.25V on a Xeon tho.
I've used the Mugen 4 with reasonable temps - however, had to mod the case to ensure decent intake airflow - with my BitFen Ghost. It's a quiet, restrictive case - limited to 160mm high cooler - hence the 158mm Mugen 4, which I got on sale. The Mugen is good with the stock fan, but ended up using 2 EK Vardar F3s on it to support decent overclocks. After getting 2x $20 fans, it's not a bargain cooler. Went from mid 70s under IBT at 4.25/1.31V to mid 60s after case mod/2 Vardars. Ambient temp 21C, cooler intake temp 24C.
The only bargain cooler I'd consider now is the new(ish) Thermalright TS140 Rev A. which at
$39.95 from Nan's is the best cooling deal atm - It's a large single tower with great performance from its quiet 140mm stock fan to support a decent overclock - 4.2 is the start of decent for me.
I'm migrating the Sabertooth/Xeon into a HAF XB, which has great airflow (with 2 140mm Noctuas intakes) and will be using a D15, because cooler height is no longer an issue. Yay! The top tier twin tower coolers are the best choice in air for overclocking headroom. I went with the D15 (and NM-I3 mounting kit - free from Noctua - just ask) because it comes with two A15 PWM fans - in the tippy top tier of 140mm fans. The D14 is great, but the non PWM fans and mismatched 120mm/140mm combo isn't as quiet or as cool as using 2X A15s. And I managed to wrangle the D15 for $15 less than a D14. So there's that.
Don't have temps yet as I'm modding the fugly out of the HAF case first. Will report back, but expect the D15/HAF to best my 2 Vardar Mugen/Ghost by at least 5-6 degrees with more OC headroom.
On the waterfront, the only AIO to consider, imo, is one from trusted companies with custom loop experience. (Won't mention the hideous unreliable pumps, crappy high fpi aluminum rads and MB watering agony I had with a few Aseteks in the past - oops, I just did). And these Aseteks with high FPI rads require fast loud fans to barely beat the best air coolers. The H100i can best the D15 by 1-2 degrees, but it's 5X times louder. Ouch! Not worth the ear pain. If some pretend water-cooler cooler is 5X louder, it better be at least 15-20 degrees cooler and make espresso in the morning. When the fans on most of these AIOs are turned down to civilized noise levels, <40dB, then the D15 will best them by 5-7C. And still be quieter.
Of the AOIs, my picks are the Swiftech 220x/240x and soon,
EK Predator. The later is pricey, but is actually the only AIO I would ever buy again. Copper rad, Vardar F4ER PWM fans, Supremacy block, DDC PWM Pump. Basically their quality custom parts in a pre-assembled loop. And the option to expand the loop for GPU cooling.
tdlr;
My X56XX cooler picks:
Bargain air cooler: TR TS140 Rev A
OC'd twin tower beast cooler: D15 (with X58 mounting kit)
AIO: EK Predator