I presume the +3 Sp. Atk boost IS confirmed, right? I saw somewhere that a person tried it out by using three Tail Glows in a row and the third said "Its special attack won't go any higher!" That doesn't necessarily mean it was 3. Could've been 4.
But I doubt they would ever go to +4.
yea, it hasnt ben CONFIRMED to be 3. but it is either 3 or higher.. so it very well could be 3, 4 or 5. i highly doubt it is higher than 3, but knowing it has the possibility is comforting. either way a +3 boost is ridiculously good.