Knowing how good the Berserker was before the Chainsaw was nerfed, and with the likely fact its going to be brought back, I'ma say he doesn't need a boost in either resistance, health or armour.
The Berserker's skill comes from dodging specimen attacks and striking when the oppurtunity arrises. I used to play medic with the axe alot so making the swap to Berserker wasn't that hard for me. In any case the Berserker doesn't need more resistance. He is a wrecking machine, but is very hard to master. Players need to pick their moments carefully to ensure they don't get hit.
The Berserker when played properly does better than the medic, just because he HAS a damage resitance doesn't mean people should be using it. Its why these *Medic is better than Zerker" threads always make me laugh. Players can be more sloppy as a medic, but they can't outshine the Berserker as a crowd controller. The resistance is there to help him IF he makes a mistake, and allows him to get away with those mistakes more frequently than other classes. The principle however remains the same as it is with any other class. Strike fast, and avoid taking ANY damage.
Stepping in and chopping down 1 or 2 zeds then retreating and re-analysing is the best way to play, since you MUST be very alert of your surorundings. e.g. the chainsaw, while it slows the player down its primary fire "fends off" spemicens from cleanly getting an attack in. Especially in the case of clots and gorefasts it helps keep them at bay, and the only thing slowing it down is the headshot multiplyer.
Bottom line, the Zerker with the Chainsaw fix is going to be very powerful, and don't forget alot of the community is driving for everything else to be nerfed down to a certain level. IMO this change would deifnately make the Zerker not jsut a little overpowered, but massively overpowered.
Its a very hard class to master, like the Firebug, but once mastered it is a very valuable asset to the team.