I've had the HPFP replaced twice in 4 years time (120.000 KM)
I've read on the net that the 'software upgrade' for the N54 problem is more like a down-tune of the max performance delivered/requested from the pump.
It fixed my startup problems for a few months, but eventually the pump had to be replaced anyway.
Also, I've had like 20 engine limp conditions in the past 4 years. Dealer never really clarified why, but I suspect related to HPFP.
I drive european 335i, on 98 RON premium gas, so type of gas has nothing to do with HPFP problem.