It depends. One thing is for sure, if your 60' time drops your e.t. should drop as well. A small drop in 60' should equal a much more significant drop in e.t.
Your mph at the end of a run (in any given car) is largely determined by HP. If you have a mod like gears or a torque converter, your HP will not increase, but you will make the 1/4 run faster. Gears or a converter would also get you out of the hole faster, resulting in a lower e.t., but at the same mph. However, if you significantly reduce the weight of your car, your mph can increase as well; another case is if you are having traction issues. If those are resolved it can result in a higher mph as well.