Well I did crunch the numbers when the scheme came in;-) My advice then was to go variable as I thought rents were undervalued. Now I am not so sure they are undervalued.
Here is my thinking...usually rents and house prices are highly correlated. So if rents go up, then presumably you will be making a capital gain. If rents stagnate or go down, you are losing money on the capital value as well or breaking even.
So to my way of thinking, fixing the rate removes that correlation and removes one more variable. Additionally it gives you extra money in the first couple of years when it might be a lot more useful.
If the variable rate rises rapidly you will lose on the fixed rate but you will be gaining on the house price. If the variable rate falls then you will be making on the fixed rate but losing on the house value.
So fixing is a rather cautious and risk reducing strategy - if I was buying now I would go fixed. A few years ago I would have gone variable - horses for courses I guess.
clear as mud?