yes the 190 should be able to support your demands of 300-400 hp. However, you still may come to the point where a FPR will be necessary even with the 190. Make sure you do proper tuning with whatever fuel setup you have. There is alot of other posts with info on fuel pumps so do your research and find out whats best for you. Most people don't need a 255 though.

Stolen from the AEM FAQ (since it ws the first to show up in google):

The way to determine the proper-size fuel pump is based on the desired brake specific fuel consumption (BSFC) of the engine. This term refers to how much fuel in pounds per hour (pph) the engine consumes per horsepower and is a measure of the efficiency of the engine. It is a useful term in determining the total fuel requirement of the engine.

Naturally Aspirated engines have a BSFC of .48 to .50
Forced Induction engines have a BSFC of .65 to .68

Calculating the total fuel requirement of an engine requires simple equations that we outline in the following section. You must know how much power the engine is anticipated to make and we recommend that you guess on the high end. The fuel requirement will be determined in pounds per hour of fuel flow. Since most pumps are rated in gallons/hour you must know the weight of your fuel/gallon. (The vast majority of gasoline based fuels run at 7.25 lbs./gallon.)

The equations to determine your fuel requirement is as follows:

(Power x BSFC) x (1 + Safety Margin) = pounds/hour
Pounds/hour / 7.25 = gallons/hour.

An example of this equation is:

500 hp gasoline engine using moderate boost with a 30% safety margin
(500 x .625) x 1.30 = 406.25 lbs./hr.
406lbs/7.25 = 56 gallons/hour.
If the pump that is being considered is rated in liters per hour, use the conversion factor of 3.785l/gallon. The pump described above would be rated at 56 gallons x 3.785 liters = 211.96 liters/hour.

In the fuel pump sizing, always use a safety margin greater than 20%.

To determine the size of the injectors, the total engine power must be estimated or known. The fuel pump calculations and BSFC information mentioned in the previous section provides a good understanding of the fuel requirements for an engine. The following equation will allow you to determine the requirements of your injectors:

Using the same engine as above:

((Power x BSFC) x (1 + Safety Margin))/Number of Injectors = pounds/hour

An example of this equation is:

4 CYL. engine rated at 500 hp on gasoline using moderate boost with a 15% safety margin on the injector
500 x .625 = 313 lbs/4 = 78 lbs/hr/injector. 78 x 1.15=90lbs/hr/injector

If we take the flow of the injector (90 lbs/hr) and multiply it by the number of cylinders (4), we arrive at a total of 360 lbs/hr of flow. As you can see, the fuel pump described above has enough capacity to feed the engine with a little room to spare.

Steve