SD card in CF adapter vs. CF card

Periodically people ask whether they can use CF adapters with their existing SD cards, or just get the (cheaper) SD cards to use with an adapter. The stock answer is - "You could, but you'll lose performance". We've never quantified how much you'd lose. Well, here it is.
Cards: SanDisk Ultra CF 8 GB (30 MB/s), SanDisk Ultra SDHC 16 GB (30 MB/s; Class 10). I used these because they're the same product line and have the same cited speed, although the Ultra 8 GB card is about a year older than the Ultra SDHC card.
I also tested a SanDisk Extreme SDHC 8 GB card that's about the same vintage as the Ultra CF, and similarly rated at 30 MB/s.
Reader: Kingston FCR-HS3 USB3 multi-card reader
Adapter : Jobo CF Type 2 SDHC adapter. I have another, apparently identical, adapter with a different label on it, so it's likely representative of any you'd get.
Test method: Crystal DiskMark 3.0.1 x64 on Toshiba Portege R700 running Windows 7 (64 bit). Sequential read/write speeds are what you could expect to see in a freshly-formatted card. If you just delete stuff as you go, you'll see speeds more like those from the 512K Random R/W test.

Results:

• SanDisk 8 GB CF card:
  • Sequential Read: 28.98 MB/s
    
  • Sequential Write: 12.64 MB/s
    
  • 512K Random Read: 25.15 MB/s
    
  • 512K Random Write: 1.630 MB/s
    
  
  
• SanDisk 16 GB SD card (SD reader):
  • Sequential Read: 41.26 MB/s
    
  • Sequential Write: 39.39 MB/s
    
  • 512K Random Read: 37.15 MB/s
    
  • 512K Random Write: 3.664 MB/s
    
  
  
• SanDisk 16 GB SD card (CF adapter):
  • Sequential Read: 9.087 MB/s
    
  • Sequential Write: 4.138 MB/s
    
  • 512K Random Read: 8.056 MB/s
    
  • 512K Random Write: 2.114 MB/s
    
  
  
• SanDisk 8 GB Extreme (30 MB/s rated) SD card (CF adapter):
  • Sequential Read: 8.948 MB/s
    
  • Sequential Write: 3.919 MB/s
    
  • 512K Random Read: 7.920 MB/s
    
  • 512K Random Write: 1.229 MB/s
    
  
  
• SanDisk 8 GB Extreme (30 MB/s rated) SD card (SD reader):
  • Sequential Read: 41.71 MB/s
    
  • Sequential Write: 35.86 MB/s
    
  • 512K Random Read: 36.85 MB/s
    
  • 512K Random Write: 2.679 MB/s
    

Jon,

Thank you for taking the time and making the effort do this!
I asked this question just a few weeks ago......and now am glad I bought the CF card instead of going the cheaper route.

let's see more adapters! Some have "UDMA" labels on them....

Buy me one, then. :{)#

I doubt it'll change the basic fact that the adapters slow the cards down though.