Your question is like asking "What sort of insurance is a Ford, high or low?"

The injectors are available in varying impedances and chassis types. Siemens are just teh manufacturer and they make hundreds of different injectors, just like they make hundreds of different car parts, ecus, sensors, etc.

As a guide to work it out for yourself:
Multiply LBPH x 10.2 to get an approximate rating in CC's.

When choosing an injector to suit power output, its sensible to leave 30% injector pulsewidth free for "ultimate reliability" but this normally requires excessively sized injectors. (Assuming BSFC of 0.62)

As an example.
For 500bhp you will need a 100lb per hour injector if you wish to leave it OEM reliable with the full 30% free. This however is not what i personally prefer to work with and i find 15% acceptable. That makes your 72lb siemens a 450bhp injector if pushed to 15% when assuming a BSFC of .55.

For teh same 450 engine you will need a pump that can flow 170 litres an hour at the same fuel line pressure as you expect to make the BHP if you want to retain a nice 30% safety margin, and you should. On Most YB engines that pressure is 5.5bar absolute if running 2 bar boost to achieve the power.

Once you have worked out the above, your choice is no longer complex, but the big problem is working out your BSFC as it can vary wildy from 0.45 - 0.70 and it makes a HUGE difference to the injector and fuel pump rating.

Alternatively, you could just pay tuner prices for your injectors and let them choose for you, thus safeguarding your engine...