http://1000bulbs.com/product/3163/BH-E240RS120MC.html they have good reviews and good price, ballast factor .85 and input power is 74W so calculated lamp wattage is about 35W each, this is the highest lamp power available these days
installed 10 sylvania design 50 lamps and 10 phllips Alto C50 F40T12's on normal .73A advance magnetic RS ballasts and none of them work when its humid or below 20F this is a huge problem as there is only light from the remaining F34T12 GE/CW lamps which is very dim and they take forever to warm up!
so we sat down and decided to bite the bullet and buy electronic RS ballasts, these have a 600 OCV and should start lamps down to 0F just like the GE pro- line electronic RS i installed which has 600 OCV and no EOL cut either
in the tests i did with converting the inner set of lamps to electronic T12 it always started no matter the temperature without flicker and warmed up the other 2 T12 lamps on the magnetic RS ballast which always started within 10 mins
so basically i am buying 10 of these Howard ballasts for the inner set of lamps to be converted
the reason i didnt convert to T8 was because i would have to buy 18 more lamps to do the inner set in all the 4 lamp troffers and that would cost more and be more complex using different lamps