Would like to try 50/50 meth/water but not sure how well they mix and how consistant the tune will be.
Don't know if you meant 'how well a mixture would work as an injection medium' or if you actually meant how well they physically mix together, but I'll go ahead and answer the latter, since I actually know the answer
As for the first, I have no experience with alky injection on our cars (though I hope to soon).
If you're worried about how well methanol (CH3OH, or often shortened to MeOH, aka methyl alcohol) mixes with water (its 'miscibility' in technical jargon) you don't need to be at all. For the alcohol group their miscibility in water is very strongly correlated to the length of their carbon chain. Methanol, having pretty much the shortest carbon chain (only one) is completely miscible with water, meaning it makes stable solutions in all proportions (0.000001% meth to 99.9999999% meth). Even Ethanol (C2H5OH, aka ethyl alcohol) which is also completely miscible with water has a slightly longer carbon chain (at 2).
So basically, you never have to worry about any mixture of ethanol/methanol with water separating out into its component parts. the only way to separate the two once mixed is through distillation, and even then, its physically impossible to render them into their previous pure components, you'll always have a little water left in the alcohol, and a little alcohol left in the water.
As an interesting side note, partially due to their intense miscibility, if you have 100ml of ethanol and 100ml of water, and mixed them together, the resulting solution would NOT have a volume of 200ml, it would be slightly less (like maybe 190ml). the different sizes and polarities of the molecules allow for them to fill on the spaces between the other solute. Kinda like how if you have a a gallon of medium rocks and a gallon of sand and mix them together, you don't end up with two gallons, since the smaller sand will fill in some of the 'wasted space' around the rocks. Still, when you perform the mixing, especially in large volumes, it always throws you off to see a lot less fluid than your brain tells you should be there