Say I had a 2GB Kit (2 x 1 GB sticks) of OCZ DDR2 ram which is rated at 5-5-5-12
and another 2 sticks, exactly the same brand and part number but rated at 5-5-5-15.
As I understand it the 5-5-5-12 pair is the faster yeah?
So ... can I use both pairs on the same mobo and just set the 5-5-5-12 pair to run at 5-5-5-15?
The timings are close where that shouldn't be any problem. They should be the same type as well as voltage range when mixing however. You wouldn't use standard with performance memory for example.
First you will want to look over each pair's own specs as far as the voltages as well as what the board itself looks for. On the board here the user manual showed something different then seen on the manufacturer's supported memory list for the exact same board.
While the list showed 1.9v memory the board actually runs on 1.5v - 1.65v memory. The listed 1600 ran stock at 1066 and oced to 1333 while the stock 1600 runs at 1600 and can oc to 1800. Some have manually adjusted the voltages for a second pair when mixing to see things work out. Caution is advised for that however.
W7 Ultimate x64/W10 Pro x64/W11 Pro Triple Boot - Main PC W7 Remote PC Micro ATX W7 Pro x64/W11 Pro
CPU
AMD Phenom II X4 975 Deneb 3.6ghz - 965 2nd remote pc
Motherboard
Gigabyte GA-790XTA-UD4-Gigabyte GA-880GM-D2H remote pc
Memory
Kingston Hyper X DDR3 1600 1.5v 16gb - Hyper X Fury 8gb 2nd
Graphics Card(s)
MSI HD Radeon 5750 1gb - MSI HD Radeon 6450 on mini tower
Sound Card
Creative Labs X-Fi Xtreme Audio P - Realtek onooard 2nd case
Monitor(s) Displays
ASUS VW199T-P 19" HP 2082a Main-HP 2082a 20" remote pc
Screen Resolution
Asus 1440x900 - HP 1600x900
Hard Drives
WD Black 1TB HD per OS W7, W10, and pending W11 presently on 500gb OS Drive - Pending Triple 1TB HDs for Spanned Storage/backup volume
Single 2TB external USB enclosure, single 1TB System 7 Host/Boot drive, Pending 8TB external HD for system image b
PSU
Corsair 750TX - primary / Corsair CX600 - second
Case
Antec 900-2 - SSD compatible / NZXT Vulcan mini tower