Combining 1066mhz and 1600mhz Tri-channel DDR3 on Dell about to buy

Hello,

I am about to buy a Dell with:

I7 with x58 chipset.
Memory capacities are:
Up to 24GB Tri-Channel 1066MHz DDR3 SDRAM6 - 6 DIMMs1
Six (6) user-accessible DIMM connectors, Installed in three for Tri-Channel memory performance.

It comes loaded with 3gb of DDR3 1066mhz. These should occupy 3/6 dimms.

Dell has three the memory options below. The prices at NewEgg for additional memory are much cheaper....pasted a couple below. I would prefer to save money if possible.

My question: Could I purchase 1600mhz DDR3 and put it in 3 dimms still available? If so, will I get the full performance of the 1600mhz or would it do something like cycle down to 1066mhz as that is the speed of my slowest RAM(as this system comes with 3gb of 1066Mhz ram). Would this cause additional stress on my system causing it to fail earlier?
What are the advantages/disadvantages of buying 6GB of DDR3 at 1066mhz vs 6gb of DDR3 at 1600mhz, installing these in the remaining 3 DIMMS and combining with 3GB of DDR3 at 1066mhz which occupy the the other 3 Dimms?

Thanks in advance.



3GB DDR3 Tri-Channel SDRAM at 1066MHz - 3 DIMMs [Included in Price]
4GB Dual Channel DDR3 SDRAM at 1066MHz - 4 DIMMs [add $50 or $2/month1]
6GB Tri-Channel DDR3 SDRAM at 1066MHz - 6 DIMMs [add $150 or $5/month1]
8GB Dual Channel DDR3 SDRAM at 1066MHz - 4 DIMMs [add $250 or $8/month1]
Dell Recommended
9GB DDR3 SDRAM at 1066MHz - 6 DIMMs [add $300 or $9/month1]
12GB Tri-Channel DDR3 SDRAM at 1066MHz - 6 DIMMs [add $450 or $14/month1]
24GB Tri-Channel DDR3 SDRAM at 1066MHz - 6 DIMMs


G.SKILL 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Triple Channel Kit Desktop Memory Model F3-12800CL9T-6GBNQ - Retail

* Cas Latency: 9
* Timing: 9-9-9-24
* Voltage: 1.5V
* Multi-channel Kit: Triple Channel Kit
* Heat Spreader: Yes
* Features: Compatible with Intel Core i7 series CPU for Intel X58 Motherboard
* Recommend Use: High Performance or Gaming Memory
* Parts: Lifetime limited
* Model #: F3-12800CL9T-6GBNQ
* Item #: N82E16820231225
* Return Policy: Memory Standard Return Policy


Crucial 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1066 (PC3 8500) Triple Channel Kit Desktop Memory Model CT3KIT25664BA1067 - Retail

* Cas Latency: 7
* Voltage: 1.5V
* Multi-channel Kit: Triple Channel Kit
* Heat Spreader: No
* Parts: Lifetime limited
* Labor: Lifetime limited
* Model #: CT3KIT25664BA1067
* Item #: N82E16820148246
* Return Policy: Memory Standard Return Policy



* Original Price: $124.99
* You Save: $5.00
* Free Shipping
* Your Price:$119.99


Combo Special


*
* Your Price:$134.99

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Module Description Description Product Code & SKU Product Code & SKU
Studio XPS 9000 Studio XPS 9000 435TH [224-4399]
Operating System Genuine Windows® 7 Home Premium, 64bit, English W7HP6E [330-6097][420-6436][420-6576][420-7938][420-8873][420-9691][421-0323][421-0530][421-1183][421-1603]
Studio XPS 9000 Intel® Core™ i7-920 processor(8MB L3 Cache, 2.66GHz) MI7920 [317-0067]
Memory 3GB DDR3 Tri-Channel SDRAM at 1066MHz - 3 DIMMs 3G1063D [317-0071]
Keyboard Dell USB Consumer Multimedia Keyboard MMK [330-0915]
Monitor No Monitor N [320-7810]
Video Card ATI Radeon HD 4350 512MB AT4350 [320-8143]
Hard Drives 500GB 7200 RPM SATA Hard Drive 500S [341-8516]
Mouse Dell Studio Optical Mouse SOM [330-3826]
Modem No Modem Option N [313-3607]
Adobe Software Adobe® Acrobat® Reader 9.0 Multi-Language AAREAD [410-1867]
Optical Drives 16X DVD+/-RW Drive W7DVDRW [313-8757][313-8916][421-1412]
Sound Card Soundblaster® X-Fi™ Titanium VXFI [313-7878]
Speaker No speakers (Speakers are required to hear audio from your system) N [313-4514]
Network Integrated 10/1000 Ethernet

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