Variable pay means it will come out of your bonus
Pre-tax 401k means the contribution is not taxed now, but when you withdraw instead.
Roth 401k means the contribution is taxed now but now when you withdraw
Now just mix and match.
And which one do you choose and why?
Base pay pre tax 401k
Variable pay pre tax 401k
Base pay roth 401k
Variable pay roth 401k