You can keep the DPS and damage the same as it was before. So grens would preform exactly as they did before, but would be less vulnerable to nades and indirect fire.
Sigh. Let me explain this to you.
4X80 = 320 - that's what one grenadier squad health
6X80 = 480 - that's the health of one conscript squad.
Cons having more health means MORE dps is needed to kill them at the same rate as a 4 man squad.
This isin't exactly true since grens have the survivability of 4.4 models againts small arms, while cons have a 5.5 survivability.
If their DPS would be equal, cons would win every time.
As it stands now, grens need to do 50% more DPS just to match cons. (Which they already do)
http://www.coh2-stats.com/compare?utf8=%E2%9C%93&squad1=conscript_squad_mp&squad2=grenadier_squad_mp&commit=Compare
If grens had 5 men, grens would only need to have 25% more DPS to match cons.
Grens being 5 man without any other changes like LMG and DPS nerfs would make them beat conscripts and riflemen at all ranges, early, mid and late game.