The Hiblow 200 should be a good choice according to the one pump curve I found on the net. There seem to be a few that vary, so posting the curve for your specific pump would prove more absolute. It can certainly put out the 3 psi needed to pump down to 6 foot deep water and push enough CFM to run the 4 diffusers...BUT, that 100 foot of 1/2" line is consuming a lot of the pressure that the pump can put out. In order for the pump to operate at 4 CFM (1 CFM per head, Matalas can certainly use more), the pump would be putting out about 6.5 psi. This is assuming no line or plumbing restrictions. 100 foot of 1/2" line consumes (or requires) and additional approximate 4 psi. That severely reduces the CFM being supplied to the diffusers and takes the pump out of the recommended operational range. This means the pump is trying to put out 7 psi (3 for the depth and 4 for the line loss). That puts the point on the curve off the recommended line which correlates roughly to 3 to3.5 CFM. Most diaphragm diffusers work well at 1 to 2 CFM. These rough calculations do not even consider the psi requirements for any check valves, control valves, or fittings. Add those into the mix and you just gets worse for the CFM supplied to the diffusers.

Bottom line is...3/4" id line would get you in a much better place (1 psi loss compared to 4)...1" would be more of a guarantee (0.2 psi loss). If it where my decision, I would need to know the size of the pond (volume in gallons) and It would really come down to how much price difference there is between the 3/4 and 1" line. Either way, it appears that the pump would be working a ways off it's maximum performance curve with the 3/4" line and I would consider it undersized to some degree, but not so much that it could not work with the proper line size and plumbing. Larger line just increases the CFM to the diffusers hence more water movement.

The above is based on the one curve I found. Post the actual curve for your pump and we can get into it a bit deeper.