I've mixed silicone oil for differentials with no problem. Don`t see why shock oil would be any different. Even if they do seperate, it shouldn`t take much driving before they`re mixed again.

Silicone fluid is a bit pricey, and can add up if you are experimenting with different viscosities. As you probably don't want lots of partially used little bottles sitting around, you could buy 7K and 1K and mix them:

Viscosity 7K / Viscosity 1K / Target Viscosity

0% / 100% / 1K
36% / 64% / 2K
56% / 44% / 3K
71% / 29% / 4K
83% / 17% / 5K
92% / 8% / 6K
100% / 0% / 7K

For those interested, this comes from the following:

100Log(Tv) = XLog(Av) + YLog(Bv), where:

Tv = Target Viscosity
X = percentage of Fluid A
Av = Fluid A viscosity
Y = percentage of Fluid B
Bv = Fluid B viscosity

Note also that Y = 100 - X

If we use 1K as one weight, the volume can be easily simplified to:

X = 100Log(Tv) / Log(7) and of course the amount of 1K is Y, which is = 100 -X

These calculations can be re-done for 10K and 1K to get a bit more range.

A useful (blend calculator) link is:

http://www.eion-additives.com/support_visblend.htm

Just set the Interaction Parameter to 1.0 when you use the caluclator.