In my Eberron campaign, I use rakshasas regularly. Personally, I "correct" their CR to 8. Note that in the Eberron book, the zakya rakshasa which exchanges sorcerer equivelent levels for fighter equivalent levels and a better layout of attributes is a CR 8. With SR about 24, Str of 18 or so, a DR of 15/good and piercing and True Strike 3x per day + chill touch and vampiric touch 1/day or so, in addition to bonus fighter feats and heavy armor and a shield, a zakya can be a tough fight.
MM rakshasas are effective against parties up to about 8th level maximum, and that is pushing it. The rakshasa's third level spells are a joke beyond that, and it has nothing else to rely on for offense. In my experience, in a fight they tend to get overwhemled and slain.
Defensively, their SR is excellent right up until the PCs use spells that don't give SR, and the DR is similarly great against poorly equipped, low level parties but breachable by better equipped fighters. The biggest problem it has is that it doesn't have good enough hp and defenses for a creature of CR 10. It is plenty good at a CR 8 though.
I figure if:
a) 3e assumes that NPC Sor7 has the same CR as NPC ftr7.
b) DMG rakshasa is similar to Eberron Rakshasa zakya with a couple of swaps: swap rakshasa's 17 cha for zakya's 18 str and assume that the slightly higher SR of the rakshasa is an even trade for the effective spell-like abilities that the Zakya gets + a better Con. (Personally I think the zakya gets the better of that trade off).
then it follows that:
c) The rakshasa and the zakya should have the same cr which I argue is closer to the 8 than the 10. Or if anything the zakya with the greater hp, higher AC (it can use heavy armor) and the overall better combat layout should have the higher CR. Instead the zakya's is a reasonably 8, and the rakshasa's is a ridiculous 10. Go figure.
Tzarevitch
P.S. My representations of the Zakya and the MM rakshasa may not be 100% accurate because I don't have the books in front of me, but I am sure they are pretty close.