In general, no, Amperage rating alone is not a valid indicator of a given stepper motor’s specifications for a specific duty such as an extruder motor.
You have to know the system and any limitations and requirements.

#1 the stock melzi board uses built onboard A4988 drivers that I consider an absolute max reliable current limit of 1.5A. Yes, the chip might have a higher rating, but thermal design of the board, the housing, the fans, the vents, and usage all come into play. Thus, I smartly de-rate the drivers to a sensible 1.5A

#2 stepper motor torque rating is a function of all 3 components. The stepper driver, the motor coils, and the rotor length and field strength of the magnets. NEMA17 is just an outer size specification and mounting pattern. Length of the motor is one of the variables and in doing so, determines the stack makeup of the rotor and how many magnets are involved. The coils produce the rotating magnetic field, but the field must be attracted and resisted by the rotor field.

#3 Just as the physical parameters matter, so do the electrical. Since we are talking about being driven by a current limiting and microstepping driver, it’s imperative to understand the relationship of the power supply voltage, the driver internal chopping function, the motor coil inductance and thus resulting resistance. The higher the inductance rating, the slower the motor can spin because the coils take time to energize and reach rated current. Resistance also limits the voltage and current and largely translates power to heat. Some chopping drivers do not react well to extremely low inductance and resistance (often found in higher current rated motors).

The bottom line is there is a very limited range of motors that will work well as an extruder motor in an i3. You want greater current than 0.8Amp, but less than about 1.3A as the upper limit. You want a motor about 5 Ohms or less but not less than 2.5 Ohms. It should be longer than the current V2 motor, but longer motors begin to cut into the X usable distance because they hit the frame on the i3.