Another question about pre-race warm up

This question is about the intensity of the pre-race warm up rather than the distance covered. How hard do you swim in your warm up? 70%, 80%, 90% effort? My thing is that I like to descend my times in practice. If I want to swim a really good 50 in practice, then the 50 prior to the ALL OUT, RACE PACE, FOR YOUR BEST TIME effort should, ideally (for me at any rate) be within a second and a half of that time. I have to work myself into a sprinting frame of mind. I need to do at least three or four fast ones before I go REALLY fast. On the first I might concentrate on the catch, the second keeping my head down, the third my legs and on the fourth the turn. Then on the final one I put it all together and go ALL OUT. I think it is as much about getting myself into the right frame of mind as it is about physically warming my body up to the full sprint. But I have very little Masters Meet experience. In fact, I have only swum in two Masters meets. At the first one (just over a year ago) I didn't really know what to do and at the last one (six weeks ago) there were so many kids in the pool I gave up and didn't warm up at all. I am swimming again this weekend. I don't want to over exert myself and was wondering what other sprinters do for their warm ups. I am not worried about warming up for the 200 free, though. A relaxed 500m followed by some fast but controlled 100's with good rest in between always does the trick for me.