Question

maximum speed of virtual particles

Answer 1

though a vaccum its or 299 792 458 m/s this can be shortened or rounded to 300 to solve for Lambda

Answer 2

technically speaking you can go faster than light...

Answer 3

If we say that a virtual particle for gravity is a graviton, then due to its lack of mass it can and by the SubQuantum Kinetics theory do have a velocity hundreds of times faster than light. Although in SQ-K there is no graviton, an effective gravitational wave moves faster than light.

Answer 4

Sub-quantum kinetics though is not considered by most physicists as being a correct formulation of nature.

In most conventional physics, the speed of virtual particles measured in any inertial system will not exceed that of light.