I'm not going to run the numbers, primarily because the variables have rather wide ranges. Instead, I'm going to touch on how the change will feel.
Under the normal system, where dice can theoretically explode forever, there is an increasingly remote possibility of a success on any Test. Obviously the chance drops of significantly for each explosion required, but it's at least possible.
When reducing die pools, you eventually get to a point where you run out of dice. If you have nothing to roll, you obviously can't succeed.
That said... even without the specific percentage chances, players tend to have an idea of how it works. During the years I played SR2, most players wouldn't even bother to attempt a roll with a TN higher than 10 or so, except for knowledge-type checks. They knew the chances of a useful success (more than one "hit", to use a later-SR term) were slim to none, so it wasn't worth wasting the time at the table (obviously Damage Resistance Tests and similar were a different case).
Your system will increase the number of "slightly off spec" rolls that occur - two or even four dice may not be a big deal if there are applicable die pools. I don't think it will have any bearing on the "way out of left field" rolls.