Fonsini
I will attempt a semi sensible answer. Usually within 1nm horizontally and 200' vertically is sensible. Whatever you do, don't go blind.
When crossing the pond it is normal to have a bigger block of airspace to allow more width. Provided you're VMC of course.
On the Jag we never got high enough to have to worry about RVSM but in the Hawk we do regularly. Those that are not RVSM compliant will only be alllowed up there if it's not busy since they need more vertical wiggle room. Those that are will typically stick with the rules I mentioned above.
I have no idea whether Vipers are RVSM compliant or even what the USAF do on ferries. I imagine it's similar though.
BV