True, you went from 4 mgs of xanax to your current 2.5 mgs daily but inbetween you were on ativan to ease off of xanax, no real progress except ativan a little longer half life. You sound like you don't want to get off right now so I assume you and doc have a plan of your own.
ativan,xanax, or any of the benzo's will keep you from going into withdraws... You will definately find the withdraws as soon as you stop benzo's all together... It takes about 3 days to go into full blown W/D...
withdrawal from benzo's is different for everyone. some people don't have any withdrawal at all. for some people it's so horrific that they'd prefer a stay in hell over it. thats way safer is always better on benzo's and doses should only be manipulated by your doctor and under their supervision.