Your sisal/polyester string looks good, but in my opinion it probably isn't strong enough. The rule of thumb I go by is draw weight times 4. So for a 44# bow I'd want a string with a break strength of at least 176#. The reasoning behind this is that when the string slams home after shooting an arrow, its under considerably more stress than when at brace or drawn. It will probably work for a while but if a string breaks during a shot, it's likely the bow could break too and I don't like to take that chance.
I have some linen string with a advertised break strength of 75#. If you'd like, I could send you enough to make a 4 ply bow string. That's what I use on most of my bows and I feel like its more than strong enough. It won't look as primitive as sisal but it's more primitive than dacron or polyester. I believe linen is what experts think the bow strings of old english warbows were made of but don't quote me on that. If you want some just pm me your address. Or you could get a roll of your own at pyrosupplies.com, although their site down right at this moment.
As far as the brace height issue, I generally brace a bow at the lowest brace height at which it shoots well and clears the fletching. The lower the brace height, the longer the powerstroke and the more energy applied to the arrow. At least theoretically. Also, a high brace height puts a bit more stress on the limbs at brace.
