

I made my GC4 higher by 5.5", or 35.25" final slate height.
I'm a tall player, with a bad back, and decided I wanted to try this. I've had the table for a couple of months now. Not a single roll off, and the table feels as sturdy as the GC's at the pool halls. So, no detrimental table affects of the additional height.
It is more comfortable playing most shots. However, longer shots are no longer reachable, due to the added height. My back still hurts playing, but I think I can play longer periods of time before it gets too bad.
The blocks added 4.5" of height. The feet added 1". See This Feet Link for more details on the feet:
Thanks to the mechanics who answered a few of my obscure questions this past year so that I could design these, without the table in front of me.
The below posts has more info on the riser blocks.