Well, let's presume you're a T3 class with a +1 glyph prep and you're using the Pactmaker's spirit pact. It's a fair presumption that you will retain one glyph in the end-game, so you'll convert 6 glyphs at 90 a pop for a total of 540 CP.
For item conversions Then let's say you use translocation scroll for a 100 CP item, from shops you acquire soul orb , venom ward , bloody sigil , and a Keg . I'm sure more is possible if you can manage a total buy-out, but this should still be a high-end estimate of what can be expected from a conversion-heavy shopper. We'll add a 35 CP blacksmith item to round it out, though I suspect the vast majority of characters would be better served by a perseverance badge whose effect is the equivalent of 100 CP for a human. Accounting for the spirit pact, that's 460 CP.
So it looks like 1000 is our realistic upper limit. You could probably eke out a bit higher if you really push it, but I suspect this is the most you'll get under normal circumstances. Let's take a look at the relative gain offered by the 300 point sensation stone in these cases:
Human: +100% / +130%
Elf: +14 / +18
Dwarf: +12 / +16 (per level)
Halfling: +12 / +16
Gnome: +11 / +14
Orc (new): +20 / +26
Orc (old): +36 / +55
Goblin: +95 / +180
This only becomes a serious issue with stacking bonuses. In the case of halflings and gnomes this is really on par with the kegs for effect, and you'll probably get better returns out of alchemist scroll or mage plate for those races to boost the effectiveness of your potions. Humans, elves, dwarves, and new orcs are hit by diminishing returns are will be better returns from investing in other things.