I don't have any real problem with Halal slaughter where a reversible stun is used, although I'm not sure whether you're aware of the fact the halal process is designed specifically so that death is the result of exsanguination. They aren't killed instantly, even on a perfect kill they aren't killed instantly so I've no idea where you get your information, but it's wrong.

Without stunning an animal will die in around four seconds in a perfect cut, which rarely happens. In many instances an animal may feel conscious pain for up to 30 seconds after the cut is made. So what I do have a problem with are the twenty or so abattoirs in Australia that slaughter both Kosher and Halal without stunning under religious exemptions. Yes these are far less than those slaughtered with a reversible stunn, but at the end of the day, and even on very conservative estimates, we're still talking thousands of animals each year. I also have a problem with the many unstunned halal slaughters occuring in countries such as brazil where unstunned halal slaughter does occur in very high volume.

http://www.mla.com.au/Research-and-development/Search-R-D-reports/RD-report-details/R-and-D-Report-D...

Also if you read Temple Grandins work you'll also see her finding show pain is far less likely in Kosher slaughter than the Halal method (which is different)

A study done in New Zealand in 2009 shows that slaughter without stunning causes pain. A new EEG (brainwave) method was used, which can determine when an animal is feeling pain. In these experiments, lightly anesthetized calves were cut with a very sharp knife that was 24.5 cm long. The weight of the calves was 109 to 170 kg. One reason why the calves were lightly anesthetized was to prevent animal movements (movement artifact) from changing and distorting the EEG patterns. The experiments showed that the calves would have been experiencing pain during the cut (Gibson et al, 2009 ab).

The knife used in this experiment was much shorter than the special long knives that are used in Kosher slaughter. The use of a shorter knife may possibly have had an effect on the painfulness of the cut. The author has observed that shorter knives, where the tip of the knife gouges into the wound during the cut, will cause struggling. An animal may also struggle when the wound closes back over the knife during the cut. Since the calves were anesthetized, it was impossible to observe behavioral reaction during the cut. From reading the methods sections in the papers, it was not possible to determine if the wound was held open during the cut, which may help reduce pain. The knife used in this experiment was similar to many of the knives the author has observed being used for halal slaughter. The special long knife used in kosher slaughter is important. When the knife is used correctly on adult cattle, there was little or no behavioral reaction (Grandin, 1992, 1994). Barnett et al (2007) reported similar reactions in chickens. Only four chickens out of 100 had a behavioral reaction. Grandin (1994) reported that the behavioral reaction of cattle was greater when a hand was waved in their faces compared to well done Kosher slaughter. All of the cattle were extensively raised animals with a large flight zone. They were all held in an upright position in a restraint box. The results of this study clearly show that the use of a knife with a 24.5 cm long blade definitely causes pain. Another factor that may have had an effect on pain was the use of a grinding wheel to sharpen the knife instead of a whet stone. There is a need to repeat this experiment with a Kosher knife and a skilled shochet who obeys all the Kosher rules for correct cutting.