Yes, 4E has a much more linear progression of character power than 3.5. You'll start out capable of having real adventures in 4E, assuming you start at level 1 either way, which is good. Due to the incredible range of effectiveness that spell choice can determine for your character, though, a higher-level 3.5 spellcaster will wind up somewhat weaker or unimaginably more powerful than a 4e "equivalent", depending on your optimization knowledge and the degree to which you apply it. It's generally agreed that casters leave everyone else in the dust around level 7 in a relatively optimized* 3.5 environment, so I'd feel comfortable guessing that it'll happen around level 11 between editions. Educated guess, at best, though.
*That is to say, without going for the bleeding edge of power for anyone, but still making the best decisions within your concept that don't require significant deviation from the usual staples and/or sanity. So you might wind up with a spellcaster knowing Time Stop and using it to apply layers of buffs in a pinch, but you won't wind up with somebody using their knowledge of binary sums to use their first question with Contact Other Plane to ask which out of a very long list of questions they should ask with that casting. This thread is not the place to debate whether or not this works, or is a good example - let us simply assume, for the sake of argument, that this is an example of "bleeding edge" optimization, because the specifics don't matter. It should still illustrate the difference in attitude between one and the other, I'd hope.