As you found out, nothing built into the software answers that question. But you do not have to try each image until you find the one that works. According to How to update the Intel® Boot Agent on your adapter, the correct image for gigabit adapters is BAxxxxL2.FLB.
The "xxxx" part changes according to the version. For example, PXE version 1.3.50 is in BA13502.FLB.
I hope this helps.
Thank you, that what I was looking for. I did a live chat and from talking to that person my network card is/was damaged and needed to be returned. That person also said you are not suppose to choose which file it would choose it automatically. That person also said there was no way to determine which image file to choose, when you hit Update Flash it would decide that for you. I posted here because that didn't sound right to me. Someone from Intel must know how to tell which image to choose, Intell wrote and update their files lol.