So I've been doing some analysis against out similar based R&F units and some that are 20mm. (Saurus are 25mm) Disregarding the similar 25mm R&F units since they will have the similar amounts of models attacking each other... If you are pitted up against 20mm based models: 5 wide = 7 of them in base with you 6 wide = 8 of them in base with you Generally we are tougher than most units out there with T4 and we also have a good amount of attacks at A2. 5 wide would offer more ranks but 6 wide offers 2 more attacks from the front and 1 more from the back while allowing the enemy to get 2-3 more attacks on you as well. However it may be an acceptable trade-off since you are tougher than most 20mm based models. What are your guys thoughts on this?
I go 6 wide, saurus are great infantry and as you say, you want a lot of them attacking the opponent. If you are supporting them well with a Slann, attacks back won't matter as much.
If you're in combat what troops that are worse than you, you want to be as wide as possible (6 against 5 wide 20mm, 7 against 5 wide 25mm). If in combat against troops that are better (and hordes) then you might reduce their incoming attacks and retain steadfast for longer 5 wide.