For the most part I never felt character growth under the D&D ruleset, at least when applied to CRPGs, had to conform to a particular level. To me it was always more a question of balance in the sense of having enough levels, or other analogues of character growth and power, that were optimal in allowing characters to go through the game from beginning to end in a satisfying manner. In that context, I find Temple of Elemental Evil's low level cap to be perfectly reasonable, just as a level 20 cap was likely adequate for Neverwinter Nights. No game seemed to need more than that.
However, the rate is something else entirely and while I can't specify any particular lenghts, I can point out the first Baldur's Gate and Fallout as examples of a satisfying level rate. Having every level gained feel like a small victory in the face of tremendous adversity certainly contributed to it (and in a way this was more palpable in Fallout). Torment also seemed to have a good rate in the early levels.