Well, you wouldn't need to upgrade all the way to the 40 to get a noticeable improvement. The OM 20 stylus upgrades from bonded elliptical of the OM 10 to nude elliptical at about $99. The OM 30 stylus is a fine line and the OM 30 is a Fritz-Geiger.
06-06-07: Genesis168
I believe I can get a used OMP10 for a good price..but the 40 stylus...WOW! @$299. Was the OMP10 better than what was there?
So they're incremental and all about $100 apart in price. Absolute Sound lists both the OM 20 and OM 30 as very nice sounding over-achievers.
Any of them would be a step up (or more) from what's typically associated with a P-mount cartridge.