dual ddr matching - how to know?

How will I know for sure that dual ddr will work -- or is working -- in my nForce2 mobo? I want to upgrade to 2x512 for 1GB total.

I have 2 sticks of 256mb ram, bought a year separate of different brands in slot 1 and 3.

1) How do I know if they are(n't) working in dual mode?

2) Will two sticks of the same company and type always activate dual mode?

3) Some companies have twin packs for about $100 extra. Are these tested to run even better in dual mode or are they the only way to guarantee it?

4) From what I can see for sale my budget puts me at either decent sticks of 2700 for ~$80@ or CAS2 sticks for ~$100@. Will CAS 2 really make a big difference over 2.5? I need performance w/stability, not bragging rights.

The advantage of getting those matched pair "kits" is both sticks have been tested and are very close to being equal. Whereas if you purchase two sticks individually, even if the same manu/model, one may be capable of a higher overclock than the other.

I think latency timings make a big difference in memory bandwidth, but these can always be relaxed if you run into stability issues.

My impression of the kits is you get 1T timings guaranteed with the pair. I assume this is rare.

What I'm really curious about is how to know dual channel mode is even active. Dual channel mode isn't even mentioned in my manual.