would a ragtop kit be able to handle high speeds on a bug with an EJ20TT engine, I'm talking over 200km/h driving for short periods.

It's not a stock ragtop, it's from http://www.parisbeetles.co.uk/beetle%20sunroofs.htm 

it's attached to the roof with poppers up front, I could put some kind of small wind difusor just before where it attaches to keep it from flying away.

I would not do it!
You will weaken the car by cutting the roof off! For a Turbo engine it should get some extra strengh! To enjoy riding with the roof open, you can´t go to fast anyway.

strenght wise I am not very concerned since I have a full roll cage welded in and will be getting the chassis reinforements for a convertable.

I will propably put a small wind deflector on the roof just before the ragtop to keep it from blowing of the car at high speeds.

I've never driven above 130km/h with the top down in my buggy. at over 100km/h the wind makes like you feel like your hair will be ripped out.

200kmh + open top =

keep the roof. non factory soft tops generally suck big time...they also lower the value of the car and are irreversable.

That thing will leak big time.