Email from DFI HQ:

Yes, JR P45 Micro ATX board has “2 PCIe v2 x16 slots” , due to our SPEC. definition for it, we fixed 2 slot are 8X+8X supported.

Due to the design limitation, there is no jumper array or digital switch to let PCIE1 become 16X supported



But, do not worry about the 3D performance. We believed there is no a bigger performance gap between 8X/16 Gen2, even CF enabled.

Picture is the test we done on ATI 4850 for your reference (DK P45 compare to LT X38)





PCI-E bandwidth
3dmark Vantage Score
GPU Score
CPU Score
File link:

8X Single
4982
6049
3258
DK_P45_PCIE4_ATI_HD4850.jpg

16X Single
4996
6071
3262
DK_P45_PCIE2_ATI_HD4850.jpg

8X+8X Crossfire
6459
9725
3217
DK_ATI_HD4850_Crossfire.jpg

16X+16X Crossfire
6933
9643
3762
LT_X38_T2R_HD4850_Crossfire_



Have a nice day!
So, fixed at 8x full time, but they claim there's little to no performance hit for this...