Does KG's number 5 belong retired in the rafters? Yes. The end.
Ok, I'll elaborate a little more.
First of all, it has to be pointed out that Kevin Garnett's impact on the Boston Celtics went well beyond the stats he put up in a green and white uniform. With that said, Ben Rohrbach has some excellent stats showing just how great KG's stats are, and what they could be projected out over the next three years.
How Kevin Garnett cements his Celtics legacy and ensures his number retires to the Garden rafters
Scoring is one thing. Contributing across the board, as Garnett does, is another. Only three players in Celtics history have exceeded 8,300 points, 4,400 rebounds, 1,400 assists, 600 steals and 500 blocks: Pierce (22,591 points, 5,417 rebounds, 3,401 assists, 1,349 steals, 561 blocks), Larry Bird (21,791 points, 8,974 rebounds, 5,695 assists, 1,556 steals, 755 blocks) and Robert Parish (18,245 points, 11,051 rebounds, 1,679 assists, 873 steals, 1,703 blocks). Based on his projected numbers over eight seasons, Garnett would be the fourth.
Note: Those are just Celtics stats. He already had a HOF career in Minnesota and basically is having another one here in Boston. Just amazing stuff for an amazing player.