BR for 4-way play

I have a question regarding making the move to 4-way play, and it concerns bankroll. I play limit games.

The rule of thumb I've been going by is, for any given limit, buy in for 25 big bets but keep a bank roll of 500 big bets. This has me buying in a 1/2 game for fifty bucks with 2k in reserve.

Now when I start playing 1/2 4-way, I'll be buying in for fifty bucks four times.

I'm wondering do I need a larger reserve (since I'm now risking two hundred bucks at a time and not fifty)

or

will my two thousand be enough (since I'm still only risking fifty bucks at any one table)?

What's the rule of thumb here?