Kind of glad to see this thread reserected. I have used elk, deer buffalo and allot of cattle sinew, I agree with foot it is just as strong and I have had no problems with it at all. Sinew is sinew, if it is strong enough to hold a muscle to the bone that is moving a 1500 lb cow through a field is is certainly as strong as the sinew moving a 175 lb deer.
I believe preparations of sinew, surface and glue used are more of a factor then anything. In all the bows that I have sinewed I have had one lift off the surface and the was due to lack of surface preparation. That I have never had any fail by breakage. Also the soak time of sinew and sinew prep (Strands straight and refined) is very important on the amount of shrinkage and reflex that it will put in a bow
Cattle sinew is easier to get as well. I have had some that seemed slightly greasy but do not know why