If you are a bug guy like me I suggest you keep to 26" rear tires or less..
Since bigger tires change your drive ratios it puts a greater strain on clutches and engine.
I notice a significant difference between my brothers ES with 25" and mine with oversize 26"..
Hills he can power up in 3rd gear I have to keep to 2nd to prevent lugging the engine!
I've had the chance to play with a lot of tire/rim sizes on the SX and ES over time..I wouldn't do oversized 26" again, and definitely not 27"!!
As far as the smaller(width) front..it awesome how it improves the handling..highly recommended!!
Current toys..
1986 Honda 350X..trail bomb!
1985 Honda 250SX..my main mudder
1985 Honda 250ES..Back in Black Trike
Current non-trike toys:
1990 Honda TRX300FW
1995 Seadoo GTX
1998 Polaris Indy Lite 340(Nearly new looking)
1998 Polaris Touring 500
1998 Club Car (electric)