I think you've got to really vary your jabbing. Good, experienced pressure fighters will time and counter you if you just keep firing jabs to their head no matter how quick and stiff they are. Your jab is their way in so it's also a good idea to feint jabs early on to guage their reactions. Alot of guys will slip a jab to your inside looking for a left hook so if you notice them doing this its probably a good idea to circle to your left. After you've established your jab you can feint one and look to land a right uppercut. I don't know what the others will think about this but I've found that if I'm against a guy with good, quick head movement and fast feet than sometimes I'm better off looking to land a right hook to where I think his chest will be after he has slipped to the inside of my feinted jab. It doesn't matter if I miss his head with my fist because I've still got a chance that my arm will wrap around his upper body stopping him from throwing his left hook and allowing me to clinch and turn him. There's also a chance that you could unintentionally clothes hanger him and this could really give him second thoughts of bullying his way in. At the end of the day I think you want to suprise the pressure fighter with changes in your rhythm and intentions. Make him think that your going to just stick and move then all of a sudden up the intensity and land two or three bombs and push him back.