Ok, I plugged this into Beersmith with a 5 gallon boil for 40 minutes. This calculation factors that you steep the grains for 30 minutes at 155 degrees and that you boil the corn sugar and wheat dme for 40 minutes and then add the LME and boil for 15 minutes.
OG - 1.066
IBU's - 53.1
SRM - 9.5
FG - 1.012
ABV - 7.1%
If you boil all of your extract for 40 minutes the IBU's drop to 39.6. So you can see how the gravity of the wort affects your hop utilization.
Boil time will also affect your bittering hop utilization. If you increase your boil to 60 minutes your IBU's go to 59.1. Again this is if you add the bulk of your extract in the last 15 minutes of the boil.
Having a tool like Beersmith allows you to plug in different variables so you can design a beer with the hop and malt character you are looking for. I am not too familiar with the Blonde style so I don't know if you are trying to accomplish.
This might be the beer talking....but I really love beer!