Well, I am also in that situation. I am deciding to go with either the 40 or the 60.The only problem is that the 60 is about 130 bucks more. Here is what i would get

for the 4 star 40:

Sig Four Star 40 ARF Red 59.75!QUOT!
SuperTigre GS-45 ABC w/Muffler
Top Flite 10x7 Power Point Propeller
SuperTigre Sport Glow Plug Medium Heat Range
Great Planes Silicone Fuel Tubing Standard 3'
Futaba 6EXAS 6-Channel FM/4 S3004
Great Planes Easy Fueler Valve Glow
foam
MonoKote Neon Green 6'

Total is about 440

For the 4 star 60

Sig Four-Star 60 ARF Red .60-.75,71!QUOT!
necessary washers and screws
SuperTigre G-90 Ringed w/Muffler
Hobbico Y-Harness Futaba J
Hobbico Extension 12!QUOT! Futaba J (2)
MonoKote Neon Green 6'
Futaba 6EXAS 6-Channel FM/4
Great Planes Easy Fueler Valve Glow
foam

Totals to about 570


So the difference in price is about 130. However as people have been saying, the 60 size engine will go with u to your next plane.I am not sure about the G-90 in the 60 but for $120 its not a bad price. My question is, is the extra money worth it for the difference between the planes?