To see results should I train where I want my result to be? For example, on Tuesdays part of my workout is 8 x 100m @ 90% effort. Should I run at my 90%, or what I want my 90% to be? This is something that I am only trying to apply to running for now.
To answer your question in the title. No, dont train at what you want to be able to run at. Do a mile, 12 minute, or 2 mile test run at your best then use this to base what your training should be. Look up Jeff Galloway's magic mile table or use McMillian's calculator to figure out what your goal distance time would be using the test run time. This time is what you should expect to do or better. During training never run more than 60% of your goal distance at this pace. 2-4 weeks out run no more than half of the distance at this pace several times to train at your this pace.
Training at the proper paces will eventually bring you into range of achieving your goal ignoring things that are out of your control.
McMillan has some suggested goal paces you can use and I just paraphrased what he says.