Personally I think he would be almost as good, but not as good. In test matches today, there seems to be a lot more aggressiveness shown by bowlers and teams on the whole. Fielding is much better than it used to be just 20 years ago (not including Pakistan
).
In current cricket, he wouldn't have to put up with two great bowlers (Warne, McGrath) since he would play for Australia, but he would definitely have to figure out a way to counter the likes of Akram, Younis, Murali, Akhtar, Donald, etc and some more quality bowlers the likes of whom did not exist in the Don's day.
Having said that, I think he would still be the best batsman in the world, leaving the likes of Sachin, Lara, Inzi, Dravid, Ponting, etc in the dust. And with the popular trend of batting allrounders that didn't really exist back then, who knows, he may have been a good Sachin-esque bowler.