you have to be specific with your training to continue to make progress. just training the bench will only get you so far. you have to really take a close look at your training and determine what needs work.
the first step is to determine if your form is spot on. if it is, the next step is to determine weak points in your lift. for example, when i take a max attempt on bench i slow about 3/4's of the way to lockout. knowing this i hammer that weakpoint. i do so through using board presses, floor presses, pin presses, etc. i also do a lot of accessory work to strengthen my triceps.
full ROM benching, if that is what you are doing, is great but ultimately to get past a certain point you will have to address lagging areas. this is where trial and error is needed. you try a bunch of stuff and hopefully find what works for you. this is also the reason why most people never reach their full potential.
they can't diagnose problems in their training. they just keep doing a lot of the same. you know you have a good program when you can give specific reasons for everything that you are doing.
i was a bit long winded. so to answer your question- i train a bench variation for four weeks then i typically test my bench to see if it actually helped me get stronger.