well, we did see Orochimaru without the handicap. It was the fight he had against Hiruzen. This is when he definitely wanted to kill him, and relied on his summons rather than just using himself..
But that was in the early parts of the manga, before kishi decided to put everyone's powers on hyperdrive. The next time we get to see a bit of what Orochimaru is capable of is in the shippudden saga when he's fighting tailed Naruto on the bridge. In this battle he mostly shows that he can take a beating without showing any signs of weakness.
That reminds me, I don't really get how Orochimaru's cells are enough to give Kabuto this inevitable immense power though. I figured orochimaru's power was greatly due to Orochimaru's forbidden jutsus rather than his biology/experiments. After all, Sasuke pretty much gained his best stuff in his mind via genjutsu (or reverse possession).
I have a feeling that Kabuto will be really powerful when he's finally in battle but it'll be so much more powerful than Orochimaru ever was, and not even based on Kabuto's presence in the equation, but just because kishi will be inconsistent regarding orochimaru's biological power.
There was only one problem with Orochimaru's fight with Hiruzen...and it wasen't only that it was a 3 on one. The other issue was SPACE. I felt that the level of tecnique used in that fight did not so much represent the inmuturity of the manga but more the limited space in which Kishi crammed 4 of the strongest people ever to be in a battle royale. I noticed much after, that Orochimaru ,given the necesary space, and the right opponent could dish out some mayor jutsus. The thing was that in that confined space it was simply a matter of high-powered, but not-so-flashy jutsu- consider also that you have to adjust your abilities to who your fighting.Orochimaru knew alot of his flashier techs were not going to work on the bad-ass old man so he just didin't waste the Chakra. I think that Kabuto will not reach Orochimaru's "true" level of power even if his fight turns out to be more exiting than all of Orochimaru's ever were. We just never got to see an all out 1on 1 no space limitation non-handicapped Orochimaru battle that seem to predominate in Shipudden, but weren't so common in Naruto p1.