Just equate things back to 35mm terms. Shooting distances will be the same with either 4x5 or 35mm since the proportionally longer focal lengths just fit the proportionally larger film.
Your 305mm is about the equivalent of a 90-100mm lens on 35mm. Slight "telephoto" perspective, but not the dramatic compression of a 300mm.
One way to get more compression would be to use your 305 from a greater distance, and crop the image down or use a roll film back. But you seem to want enormous enlargments and feel you need to use the entire image. That is a problem since this is not what LF excels at.
A 450 (Fujinon C for example) would be more like a 135mm lens in 35mm. A bit more compression, but not the dramatic effect you seek. A 600mm lens would be about like a 180mm, pretty good compression, but now you need LOTS of bellows and probably a rail camera with 2 tripods for stability. This is not what most folks think of as a handy portrait setup.
A final choice (expensive)for compression would be the Nikkor T 800mm f/12 telephoto which would be like 250mm on 35mm. That about the limit of practicality (if you consider a $2800 lens and a yard of bellow practical).
You could use a 450mm and a roll-film back, and enlarge the 6x7cm image accepting the resulting grain. You are probably going to have to make a choice between sharpness/grain and cost/compression.