I have a 7790 GPU in my computer if I install a driver after the 12.5 beta I see the following when I load up BOINC:
03-Oct-13 18:52:45 | | Starting BOINC client version 7.0.64 for windows_x86_64
03-Oct-13 18:52:45 | | log flags: file_xfer, sched_ops, task
03-Oct-13 18:52:45 | | Libraries: libcurl/7.25.0 OpenSSL/1.0.1 zlib/1.2.6
03-Oct-13 18:52:45 | | Data directory: C:\ProgramData\BOINC
03-Oct-13 18:52:45 | | Running under account Administrator
03-Oct-13 18:52:45 | | Processor: 24 GenuineIntel Intel(R) Xeon(R) CPU L5640 @ 2.27GHz [Family 6 Model 44 Stepping 2]
03-Oct-13 18:52:45 | | Processor features: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss htt tm pni ssse3 cx16 sse4_1 sse4_2 popcnt aes syscall nx lm vmx smx tm2 dca pbe
03-Oct-13 18:52:45 | | OS: Microsoft Windows Server 2008 "R2": Standard x64 Edition, Service Pack 1, (06.01.7601.00)
03-Oct-13 18:52:45 | | Memory: 23.98 GB physical, 47.97 GB virtual
03-Oct-13 18:52:45 | | Disk: 148.95 GB total, 71.29 GB free
03-Oct-13 18:52:45 | | Local time is UTC -4 hours
03-Oct-13 18:52:45 | | VirtualBox version: 4.2.16
03-Oct-13 18:52:45 | | OpenCL: AMD/ATI GPU 0: AMD Radeon HD 7790 series (Bonaire) (driver version 1124.2 (VM), device version OpenCL 1.2 AMD-APP (1124.2), 1024MB, 966MB available, 2408 GFLOPS peak)

If I have 13.5 then I get this extra line:
03-Oct-13 18:52:45 | | CAL: ATI GPU 0: AMD Radeon HD 7790 series (Bonaire) (CAL version 1.4.1741, 1024MB, 966MB available, 2408 GFLOPS peak)

Any idea's how I can use a later driver?

I have another computer with a 7870XT and it seems to show CAL all the time?

I'm not sure I understand what your problem is? Don't you want to use a later driver than 13.5? Or don't you want to use 13.5? Or do you explicitly want to use 12.5?

That the 12.5 driver may not see the CAL portion of the GPU, could be because at that time the driver didn't know about the HD7790. This GPU is one from March 2013.

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I guess I'd like to use a driver later than 13.5 (12.5 was a typo).

for some reason all the later ones don't detect CAL?