Encoding 4k to SD very slow

Question

I'm exporting small chunks of a 1.5hr 4k R3D timeline using the default MPEG-2 encoding setting for DVD creation.  There are 2 alternating video tracks using simple edits, and about 8 audio tracks.  I changed the color/ISO in the R3D source settings, applied an MPE-enhanced color-correction filter to change brightness, and a few clips have been altered via "motion effects" to zoom in on part of the frame.
I'm running CS5 5.03 on an i7 930 with 12GB RAM and a GTX470.  I export to a sata drive that doesn't have footage on it (and isn't the C drive). The footage is on a 14TB SAS RAID-5.  I'm using the appropriate timeline for the original footage. I export directly from Premiere. I've tried unchecking boxes for maximum quality and MRQ.
It takes about 1 hour to export 3 minutes of footage!    All 8 threads are at 100% and RAM is generally around 5-10GB used. The progress window usually freezes, but the processor keeps its 100% load and finishes at the time I estimated based on previous exports.
Is this just a matter of going from 4k to SD?  Is there anything I can do to speed it up?  When I export from DV to MPEG-2, it takes less than 3 minutes.

Answer 1

Thanks, Harm.  That's sad to hear, as it presents a huge drawback in my choice to work directly with the 4k files.
If I switched to 24GB of RAM, should I expect the encoding time to drop by 1/2?  Or would it only make a small difference (for example from 1 hour down to 50 minutes)?  Can Premiere make use of all 24GB if I upgraded?
Are there settings for memory allocation that could help me now since it doesn't seem to be using all 12GB currently? 
Are there any tricks or workarounds like nesting my 4k sequence in an SD sequence or something?