I don't know specifically which compounding we used at work.
Here, however is a link to a site which shows 2 different silicon compounds with way different max temps listed.
I would say the higher temp one is to be preferred. At least for output tubes.
http://www.marcorubber.com/silicone.htm
My experience with o-rings tells me I would tend to avoid the silicon. While I doubt in home use you'd ever get one to weep, there is a binder oil as part of the compound. We used to put them in an oven at over 100c+ at very low pressure. They would weep out oil. We couldn't use them as sold to us for reasons completely unrelated to tube guys use as a damper. Later, we found a source for pre-baked rings and began using them.
Here, however is a link to a site which shows 2 different silicon compounds with way different max temps listed.
I would say the higher temp one is to be preferred. At least for output tubes.
http://www.marcorubber.com/silicone.htm
My experience with o-rings tells me I would tend to avoid the silicon. While I doubt in home use you'd ever get one to weep, there is a binder oil as part of the compound. We used to put them in an oven at over 100c+ at very low pressure. They would weep out oil. We couldn't use them as sold to us for reasons completely unrelated to tube guys use as a damper. Later, we found a source for pre-baked rings and began using them.