No, you need to raise compensation. If someone is worth 250k at Google, they may work for your company for 150k if they get 600k worth of options paid out over four years at a reasonable valuation.
A 400K investment over 4 years to earn something worth 600K over the same period which will be liquid after another 4 years - does not sound very compelling to me. If it were 600K/year, yes, that's attractive.
Your best strategy would be not to have a fixed salary, but a range of salary which you can afford with your outlay, and then seen what the potential hire can be enticed with. That way you know immediately if the candidate is too expensive for you.
Just randomly increasing everyone's salary may not be very helpful.