Hi.
I am building a jet turbine for personal use and the most common method for measuring RPM is by a hall sensor mounted outside the intake bell / magnetic ring mounted onto the shaft.
Physical parameters:
The sensor will be approx 26-30mm offset from shaft center.
The magnet is 10x3mm with a 6mm hole, Neodym diametrically magnetized, placed inside the front lock nut / over the shaft.
There will be aluminium between (1-2mm) "line of sight" which will attenuate the signal.
I have a prototype of the sensor running using a US1881 sensor but fear its too weak for this application.
So I was hoping for help choosing a correct hall sensor to use - what should I look for?
I could just buy one premade sensor circuit, they are not pricey (€20 + pp) but where is the fun it that? 
Image attached for your reference:
