I am under the assumption that higher chamber pressure results in increase in exhaust velocity. Is this true?
Yes, it is absolutely true.
On this graph you can see the ISPs (aka exhaust velocity) at different mixture ration and chamber pressure.
The higher the pressure the higher the velocity and thus delta/v per unit of fuel.
A few other parameters come into play:
- The shape of the nozzle
- The pressure ratio between the combustion chamber and the outside (the higher the ambiant pressure the lower the ratio the lower the exhaust velocity)