Best type of grease to re-lube focusing helix?

I've got a couple of lenses (a Helios 44-2 and a CZJ Flektogon) which don't focus as smoothly as some of my Pentax manual focus lenses.

I'm planning to strip them down, clean and re-lube their focusing helices over the weekend, but wondered what type of grease would be best to use for re-lubing?

I have access to silicone or lithium based grease, or could get something different if neither are suitable. Having stripped down a couple of lenses in the past, the existing grease looked most like the lithium based stuff I have.

Aside from the obvious risks (polluting the lens and camera) is there a significant difference in feel or longevity between different types of grease?

I use "Weldtite" Lithium Grease for helicoids - you only need a very small amount to get a nice movement and it should be impervious to heat from around -20 to +120 degrees C (more than enough latitude to stop it running or freezing in typical British weather).

Both the lenses you mention will benefit from a dollop of lithium grease and make them work better than they probably did when they left the factory.