Go with what you are comfterable with safety and money wise. Keep in mind that the booster function of the charger isn't meant to start an engine that has a stone dead battery. It is menat as a booster for a weak or cold battery, etc.
50 amps may not sound like alot, but you would be surprised. I used to jump my yanmar tractor off in the winter by hooking up jumper cables to my riding lawnmower, etc... worked fine, and I doubt I had 50 amps of current flow going through those cables. I had a 10 /1 / trickle/ charger that I used to use also ( when I had pulled the lawnmower down and forgot to charge it back up ).. It only had a 10 boost. What I would do is go out first thing in the morning, and let it charge for 20 minutes while I had my shower and coffee. This put some charge on the battery, and warmed it up. Then I kicked the boost on, and really never had any problems. that 50/10/2 sounds luxorius by comparison. That 10 amp charge can go a long way in a little time. A battery that is weakened by accidental drain that just can't quite turn the engine over, with about 10-20 minutes of charge, plus the boost sounds like it will do fine.
My ford 8n is still 6v, and I use that 10/1/trickle on it ( has a 6v/12v switch ), and from near dead, i can start the tractor in 15 minutes of charge.
Just my .02.
Soundguy
<font color=blue>"Thanks for the info. Am I correct that I would need the 100 amp capacity for starting a diesel? I saw a 50/10/2 charger on sale at Sears for about $35, but I am concerned that the 50 amp starting capacity is too low."