I typically don't dive Nitrox on wall dives period...especially if I am leading the group for the very reason that if I DO have to help someone at a deeper depth, I don't want to put myself at more risk. I have dove Nitrox on Punta Sur to enjoy the reef a little longer, but I did not do the throat.
cnidae...these dives are not technical dives and there is no need for doubles or trimix...unless of course you want to do a truly technical dive at these sites. The key is to watch your computer and be a responsible diver.
I am not necessarily condoning this, but it is a fact that it is not unusual for people to go into a minute or so of "deco" on this dive depending on their computer...going several minutes or more into deco is another thing...but that is a very controversial subject that I would prefer not to get into here. I will say that my computer has given me a mandatory 10 ft stop on this dive, but but depending on who you talk to, that is not a true "deco" stop by definition, it is simple a required safety stop. Regardless, I do graduated stops at 1/2 my max depth anyway, just to be more conservative, even if my computer hasn't put me into "deco." Safety stops on this dive are usually around 10 minutes for me.
Bottom line is that it is the divers responsibility to watch his/her computer and dive the dive accordingly. If you DO go into a few minutes of "deco" then do the appropriate stops and make sure that your computer totally clears you before ascending. You should try not to let it happen, and if it does, learn from it for the next time.
I always add to my briefing for this dive that no one is obligated to stay at my depth, meaning they can ascend shallow if they need to. Additionally, I have them communicate with me when they are approaching their limit, just so that we all know what is going on and I can profile the dive based on the most conservative computer in the bunch (which is usually mine...UWATECH SmartPro set on micro-level 4).
Anyway, I probably said too much...but like I said, this is a very controversial subject.
Be a responsible diver and watch out for yourself and your buddy!