you can get to 150 if you buy 4 jacksons.
If you have 4 Jacksons, what's your army composition though? I have done that too, but i had 3 Jacksons, 1 Pershing, 4 Riflemen, Major, ambulance and 1 Rear Echelon Squad. Barely reached 105 pop cap, my squads had been chopped though, i had 2 rifle squads with 4 members each.
Another time i did the same thing but with the M10 tank destroyer. Same infantry composition, but i had 6 M10s. Again, my pop cap reached 110/100.